Hi Matt! My condolences to you and your family.
Glad you’re here, seven nation army is a great first song to choose. It was mine and I am sure many others. My piece of advice is to make sure you use your pinky to fret as much as possible (where it is appropriate to do so of course), it is hard at first but you will thank yourself later. Also a good setup can make even the cheapest instruments sound good.
There are so many learning tools available today, glad you had a friend show you the reigns. Obviously a lot of us here are partial to the B2B course, but you (understandably) may not want to purchase lessons yet. I spent about a year just self learning and made pretty decent progress but I needed some structure eventually. That being said Josh’s free bass buzz videos are an excellent place to start and my favorite of the ones on youtube, talkingbass is also solid.
If you’re looking for good tab there are several recommendations on this thread: Good source for bass tabs? - #23 by Mac If you do not have a metronome I really like the “Pulse” app. Also if you do not have a tuner the fender tuner app is solid.
That would be my advice/favorite learning tools, welcome to the forum!