For both cards. Usually they will allow slight buffers. I'm quite sure if you swipe any of your cards now, it may not be able to go through.

and do check on your overdraft agreement. they may charge you interest for your overdraft.

Buffer limit is 10% of CL

Don't see why not.

there's a 6 months cool down period for credit review, so next mth should be fine

You can always ask for a temporary increase without any documents.
As for permanent increase, just salary slip may not enough, EA is the best support usually.
There's another way but I guess does not really happening now which is you keep on spend close to 90% of CL and always pay on time, the bank may increase automatically for you. Maybank was 1 of such bank. I got increase from rm3000 to rm6000 last time(close to 12 years already).