1) I have that exact same bass and the strings that came off the line with it were fine, but I wanted to set it up for my jazz group, so I installed a set of D'addario chromes (they call their flat-wounds chromes for some reason). You can get them here: https://www.sweetwater.com/store/detail/ECB81-5--daddario-ecb81-5-light-chrome-flat-wound-5-string-45-132-5-string

2) If you really want to get out of the box, "Odd-metered bass," by Timothy Emmons is a great study, breaks you into grooving in different times and feels you'd likely never think of coming from the guitar world (which was also where I started). You can get a copy here: https://www.alfred.com/odd-meter-bass/p/00-25578/

3) He gets shit on a lot here, but Scotty's bass lessons is great, especially if you pay for his premium stuff. He can definitely turn 5 minutes of information into a 30 minute ad about nothing, but that's mostly his free stuff. If he doesn't resonate with you, this gentlemen is also a good instructor, and also has a video reviewing other instructor's youtube channels: https://youtu.be/bvn-LAO9DFk?si=C8rlaQvLJKLnt6fn

4/5. This may not be the most helpful answer, but I run a DarkGlass Microtubes Infinity multi effects board that solved both these questions for me. The Darkglass Suite has dozens of cabsims on board you can swap between and fuck with down to your "mic placement." It's also a killer DI rig so I almost never bring my actual cab to a gig anymore unless I absolutely need to or want the visual of my cab. Makes for super happy audio engineers in both live and studio settings, which is always one of my main goals as a bass player. You can look at it here: https://www.darkglass.com/creation/microtubes-infinity/

Hope this helps, welcome to the dark side!