Auto loans are primarily to satisfy the mix of credit installment loan factor. The OP has an installment loan with the student loans. FICO does like to see a "major bank" card but the Capital One qualifies in that regard. FICO is not concerned with what your credit limits are in particular but simply what portion of them is being used (credit utilization). The only reason to have higher limits is in the event that life makes it necessary to carry a balance then the higher limit means utilization is not as affected.
There is an ongoing debate which has not truly been proven as to whether a retail / store card has any effect in adding to the mix. I believe the last consensus was that it makes no difference. Similarly there is debate whether 2 or 3 credit cards is better. Anything over 1 seems to make a difference. Having three and carrying a balance on only one means less than half have a balance. With 2 cards it is half have a balance.
These little tricks are only for pulling the last few points available for a maximum credit score and don't matter if you are not currently applying for credit. Utilization can be manipulated before an application and FICO has no memory of it for scoring. The best thing to improve your score is NEVER NEVER NEVER be late and let time age your credit accounts.