The problems with Canon RF apsc system is that, currently there is only 2 lenses. If you want to use prime lenses, you have to adapt the old EF lenses. Nikon Apsc is slightly better since they have viltrox prime lenses. I suggest you look at Sony or fuji apsc system instead. I do understand that canon camera has the most beginner friendly user interface, but they are not opened to 3rd parties and their own apsc dedicated lens option are worse than pathetic....unless you don't mind going for the dying eos M mount....
  

The 35mm prime, you meant the full frame lens RF35mm f1.8? It will be around 56mm in full frame field of view. Aiyoo, you didn't do research first before you jump into the system kah ? It's a costly mistake. But yeah, you should trade it in for the Sony a6400, the e mount system has the widest lens selection.

Aiyoo, don't be so harsh on yourself, I won't call you an idiot, but lazy to do research la.    As regards your question, I think there is nothing wrong to go either A6600 or A7III, again you need to know what you are dealing here. 3 years in camera term is still very new. Even older camera can take fantastic photos. Video wise is a different story la.

1. A6600 = apsc camera, it has 1.5X crop factor (canon apsc is 1.6x crop factor). So, 35mm lens will give you field of view of a 53mm in full frame terms. But the advantages of apsc are that,they are smaller, the lenses are smaller and also cheaper than the full frame lenses. They are very wallet friendly that's why usually beginners start with apsc.

2. A7III = full frame, so there is no crop factor, a 35mm lens will give you 35mm field of view. So, you won't be confused as to the focal length of the lenses you want to use. A7III might be similar pricing to the A6600, but be warned that full frame lenses are usually more expensive for the similar field of view. The full frame advantages over apsc is that, it is slight better noise at high iso setting and it has about 1 stop more shallower depth of field, which mean it gives more background blur. But that is only beneficial for you if you like to take portraits of people outdoor.
If you want to start with a6600, you may also later get the A7iii when u think you are ready to jump into full frame. You can sell the a6600 to fund the jump or keep your a6600 for better reach. On the other hand, you may want to start with A7III right away, so that you won't need to lose money again when u transition from apsc to full frame. It all comes down to your wants and your budget. All the best with your selection. 

any tech stuff all like that one, if you calculative like that better don't take this hobby haha because it hurts when you think of money.
better get a leica or even higher up brands so maybe not lose any value because leica = rolex stuff already... but again, it is hard to find buyer due to very expensive haha, niche market....
like 10 years ago i get nikon D800 full frame and hope can last long , price around 10k plus that time, now few months ago trade in with my expensive lens for new mirrorless system only worth 3k lol.... i change to mirrorless due to that camera too heavy to carry in trip, plus my phone catching up the tech for shooting low light without flash.

i only hobbist photog and only take out camera when i go oversea trip. my last camera SC actually is 5k lmao over 10 yearss 

i cannot advise you anything since i also noob, but i can tell my choices for camera and hopes this can clear your thought... i formerly use nikon since study uni, so i get used with the UI and handling of nikon.
that time was using D70s... then D800 because the first FF camera and 36mp really can lasts really long for crop photo if you shoot trash in frame, until other camera catch up and your big MP camera actually consider blur and not sharp that time, now i downgrade technically to 24mp nikon z6ii with IBIS for my shaky hands, and better ISO performance. lens also downgrade since i buy package kit lens....

was using 24-70mm F/2.8G the one of the king lens all the time, now use 28-120mm f/4 S since i don't really need bokeh so much on TRIP PHOTOGHRAPHY.... landscape only need bokeh for what 

phone use google pixel 5 because i like how the AI handle the colours better than other android phone, the downside is no better , sharper zoom but i don't need that , walk in front can zoom already.
samsung colour accuracy in low light is crap lol (i think, since i am outdated)

Yes, canon camera are usually very beginner friendly. If you really want to stick to Canon R50, there is a way to do so without costing you a bomb. that is to use adapters and buy old EF lenses. Any camera you buy that was produced in the last 5 years are really good. If the photo is no good, the problems is the user, not the camera.
  That's the beginners mentality, always want future proofing. Just get what you can comfortably affort and invest the rest in getting good lenses. Even A6000 is still good  despite it's age. There's a saying in photography world, you date the body but marry the lenses. Because we always change camera bodies but once you got good lenses, they stays.
If I were you, I will get the cheapest body, play with it and get familiar with using a dedicated camera first. Get your feet wet and know your stuff, only then you can decide later if you need those features that comes with latest camera. The A6400 is really best value for money camera body in my opinion.

And lastly, forget about future proofing, it is one of the most useless concept to apply to photography gears. Future proofing only make sense when you are buying computer/laptop because with new operating system, your hardware might not be fast enough to support it. As for the camera you purchase today, it won't suddenly slow down or stop working just because there are new camera came to the market.

Very nice bro ! That is one of the best combo for the price. Your color grading is very nice. Doesn't look like a beginner to me at all.

Composition is a bit off for my liking, but the color tone is very nice.

huh what does they said, i also don't see anything bad, maybe crop a little so the center focus can take more spot there...maybe... 
it still good shot i guess.

That depends on what is your aim for using ND filters in high noon? To get the motion blur to smoothen water effect? Or just normal portraits under the sun using wide aperture to get bokeh?

Also beware that Variable NDs usually have issues like vignetting, colour cast & cross polarization. This is more apparent in cheap variable NDs. And good ones e.g. NiSi are really expensive, at least RM1k+
other alternatives are Hoya & B+W which are 'cheaper' depending on the filter size

I haven't really use an variable ND filter before, but have been eyeing for one for quite awhile. As a matter of fact, it went to my shopee shopping cart for a few times but never pull the trigger. The one that is affordable and yet has good reputation is the K&F concept variable nd....but to be honest, due to what lego warfare said about the shortcoming,I'm not too keen about them and just use high speed sync instead.

By the way, are you sure you need ND filters? As you said you're doing architecture and street photoshoot, i would think CPL filter is more useful to you than the ND....

The 18-50 f2.8 sigma is one of the best lens for street. Just one advice, try to restrict yourself to using 24mm or the 35mm focal length ONLY when you are doing street. If helps to train your photographic vision.

As for sport, you will need something telephoto. Depending on your budget, you may look at Tamron 70-180, Sony FE 70-200 F4, Sony FE 70-200 f2.8 GM.

When I said 24mm, I meant the 24mm of your Sigma lens. Because 24mm translate to 35mm Full frame. I'm sure many articles or videos will tell you, for street, the 35mm focal length is one of the best, that's why I've asked you to use 24mm.

  I also tell you to choose 35mm, it is also because it will be translated to 50mm full frame, which is also quite frequently used by street photographers.

  I don't really like to use 18mm unless I'm doing a very large group photos (which does happens when shooting friends from my church group). So, yeah, I won't promote to others a focal length which I don't like using myself. I hope that clear the doubts for you.
Yes.

all measurement of focal length normally means FF one lol...