For Amex Platinum Charge Card, you can re-apply anytime.
You need to pay AF after start using.
If not mistaken, sign up bonus is once in a lifetime.

Hmm, this is a big topic and don't have short answer.
If you want a short answer, I will suggest to redeem expiring points into Asia Miles while you slowly learn how to play air miles.
Asia Miles has validity of 18 months and you can keep refreshing the validity with activity (almost equivalent to evergreen).

Now the longer answer, I won't spoon-feed everything here, you need to spend time google and play with it.
Suggest to start from Sg bloggers such as MainlyMiles and MileLion which are very focus on Krisflyer.

SCB WM gives you 2:1 ratio for Enrich/KF/AM.
I believe you have more than 200k WorldMiles, assume 600k, you can redeem into 300k air miles.
Fly Europe, KF 1-way, you need 42k for Y and 103.5k for J; while AM 1-way, you need ~35k Y / 70k J (assume fly Qatar).
Return tickets for both parents = 300k/4 = 75k, now you can roughly know what to redeem.
J will usually optimize your return.

Last but not least, air miles game require high flexibility.
If you traveling schedule/option is very rigid, you may face plenty obstacles.
Good luck and welcome to air miles game!

Nice list, try look into M2C Gold
The Amex should be second best for KF

Yes, many Sg cards can get 4mpd (about RM1 : 1.3 KF)
We can use 1 set of M2P for (almost) EVERYTHING, but Sg need several cards for different categories.
Also most of the cards with 4mpd are capped, you can't buy S$100k stuff and expect earning 400k miles.
There are much much more air miles players in Sg than Msia.

Much inferior compared to M2P.
10,000 "AIR MILES" convert to 10,000 Enrich
20,000 "AIR MILES" convert to 10,000 KF/AM

Also overseas AIR MILES is capped at 20k per month while local capped at 30k.
You can't spend big buying Rolex.

Not really, it is quite at par with M2C Gold with lower requirement and M2C is free for life.

Think of aum 3m first before thinking about af waiver

Haha, always read the T&C in FULL

You earned 1.1 "AIR MILES" from RM1 overseas spending
10k "AIR MILES" transfer into 10k Enrich (not too bad)
20k "AIR MILES" transfer into 10k KF
20k "AIR MILES" transfer into 10k AM

Also, "AIR MILES" capped at 20k for overseas

AUM RM3m
I think also have min salary/income, but usually quite OK as long as meeting the above

Good that you can think out of the box to maximize your earning.
This is the "correct" way to play CC game.
Suggest to test on small amount and figure out which one earns you point/mile.

Try look into MBB 2 Premier instead

I believe you mean 2.5 sen, 25 sen is crazy, Enrich will close shop in no time

Already like this since day 1 of enrich saver inception.
So far most people are able to enjoy full benefits of business class.
But heard a few complaints for being rejected for lounge access, especially overseas lounges.
Just accept it if being rejected.

Good thing Enrich is unlikely to suffer from devaluation in near future.
One year later, after next KF devaluation, you will feel that Enrich is still ok.
Two years later, you think Enrich is not bad with some sweet spot.
Three years later, you think Enrich is very good!
Four years later, another round of Enrich devaluation, the whole cycle starts again.
That's the nature of air miles game.