If can invest for AB then go ahead, you'll never regret it...
Topcoat using AB , the risk of getting frosting is so low compare to spray can types

I say its worth it since AB can do the topcoat function really well.
You are already pretty much painting anyway. Paint and topcoat have similar application techniques, only you are using different liquids.

is that Top coat is a must or optional?

Trust me ... once you start using your AB ... you wont be stopping at Top Coat only. You will be poised to start painting ur kits
I even use my AB to clean my keyboard

Once you have an AB, you will definitely not using it for top coating only. So conclusion, extremely wise choice

u got yourself a very nice gift. This is the type of compressor a modeler should get, if financially there's no problem.

Basically it's the same type of compressor u find at your refrigerator; powerful, stable, and silent.

u think it's an antique, well, it might be. But more importantly it says a fact: this compressor memang tahan lama. Mine, i think is at least 20 year old and it's working fine; more quiet and stable than compressors i saw my friends own.

since yours had been idle for so many years, probably u need to spend a little money to give it an overall service. i can recommend someone to u; he's also a modeler so u guys should be on the same wave length. He's profession is actually dealing with compressors. u can also ask him to check out the specs of your compressor: how big the air tank, how often the motor need to run, air gauge, moist trap etc etc.

it might cost u a few hundred bucks (mebbe approx. RM200); but trust me, once it's done, this thing should at least last u another 10 years. OF course, unless u think the hobby wont last that long.....

Have to be a bit careful with metallic colors (esp gold) actually.  If you gloss coat it, the metallic particles or shine may lose its lustre.  You may end up in yellow color instead.

Maybe what you can do is spray clear yellow (a few thin layers) on top of gold and then only gloss coat it......

Times Square shops hardly have any paints
the one with lots of paints is Time Machine @ Plaza Berjaya, opposite of Times Square
but that shop is having Mr Hobby paints

if u want Tamiya Arcrylic afaik Tamiya Undergroundz @ 1U has the most