riddle,
to answer some of ur concerns -
I have 35k  in my AMex Blue Cash. I started with 2.5 K, and used a lot and every six months used to increase. Amex doesn't do credit check (at least in my case) if youe request increase in credit limit. Last time when I requested they did check my credit  and didn't increase becuase I have over 100 K in credit limit for all teh CCs.
recently I called BOA and asked them to increase 15 K to 25 K and they did.At one point i used to have close to 30 revolving accounts, Now I still have close to 17 CCS. Never been late. But as someone suggested having too many cards dosen't help. I have max of 780 score. currently I have 760.
What I do is keep 5-6 cards in wallet and use them for 3 months, and keep them back and use another 5-6 sets and keep rolling. U dont want to keep ur CC unsed for long. they will either decrease ur limit or cancel it. I have over 6 cards with atleast 10 K in each one.
The formula i used to increase was - use that particular card (just that one) for long, use for everything, and after few months call bank and tell them I am thinking of buying some big items and need some increase, and they did everytime. works for me.
But beleive me, i have seen ppl with less CC and and less limits with better score and all.
so keep minimal cards and use them resposibiliy- you will have better score.