Hi Implet! Welcome onboard.
You're in awesome shape for someone who's only just now focusing on managing their money. The big caveat on all the advice you'll get here is that it depends a lot on you, your unique circumstances, and your tolerance for risk. You also need to consider what your mid-term plans are, such as purchasing a home (a huge step in adding wealth in most mustachian's journeys).
Now that that's out of the way, yes, $5000 should be more than adequate to keep on hand (most people in these parts actually keep less in cash than that, but it's a place to start) and yes, absolutely you should move the other $40k into investments. I can't pretend to know all the ins and outs of IRAs, but there are a ton of discussions on it. This one seemed to have some of the basics covered:
https://forum.mrmoneymustache.com/ask-a-mustachian/don%27t-understand-limits-on-contributions-to-ira%27s-and-401k%27s-tax/msg54755/#msg54755For the car, what sort is it and what are your plans with it? If it's efficient, dependable, and/or you're attached to it, keeping it could be a defensible position. At zero percent interest it's certainly not worth it to pay it off early. The big takeaway there is to not get into the habit of buying a new one every time the lease is up. If, however, it's a gas-guzzler that you commute in every day (btw, I didn't see gas/insurance listed), then you should replace it as soon as you can.
In terms of your credit cards, I would not cancel the BofA card. Credit scores depend, in part, upon the length of your credit. Now that does not mean you shouldn't
also get a USAA card. I have one and love it and there's no particular harm to your credit when you open it - in fact any harm from them checking your score should be offset by the increase in credit available to you. This applies to any card you might open. I would also look to them for mutual funds for your investing. They tend to have fairly low-cost funds and their phone support is terrific. Vanguard is also a very popular option in these parts, so do take a look.
I hope that helps and trust me, in the past year that the forum has been up, tons of subjects have come up. There are helpful topics all over the place.