What to do next? anything?

I just received an auto loan for $4000 from a credit union, and credit scores since early March are TU: 674 (dealership said 707 a few days later), EQ: 681 — I have 3 cards, 2 retail and 1 credit (only as auth user though) … should I/can I apply for a credit card, or should I let the loan build my credit up more? Would it hurt to get a credit card, even if I don’t NEED it now?

 

I do have a dismissed bnkrptcy from 05, and a charged-off paid Cap1 card from 05, but that’s pretty much all that’s on my credit other than the cards …. I have basically no history, which is why I wonder if a card would be good..

 

Any help would be appreciated