Request higher limits on your exisiting cards. Except maybe the Firestone card. This is better for your score than opening a new card in the short term.

Then, to be frank, you need to make and stick to a budget. Eliminate credit card debt and only put purchases on a card that you can pay off each month and then the APR won't matter.

Set payments up on autopay so you don't "feel" them each month.

Only research you really need to do is find out if your employer matches on the 401k. If they don't, open a Roth IRA. Plenty of guidance out there on how to find out what investment is best for you.