You do have a lot in here to unpack. Lets take it a piece at a time.
PHP and SQL are both useful skills that never go out of style. And there are a ton of tutorials on learning them (some good and some not-so-good).
For this part, it seems like you’ve been overwhelmed because other people on your team haven’t stayed the course. I’d love to say this was a terrible one-off, but it happens a lot. People prioritize lots of stuff ahead of the start-up grind… usually because they can’t see far enough into the future to see the potential and it scares them.
Kudos to you for taking on the added responsibility. Now, find ways to simplify and bootstrap the whole process so that you don’t make yourself sick with “a month of 16 hour days”. I’d recommend checking out From Idea to Web Startup in 21 Days: Creating bacn.com, which was a short read and had a lot of great stories on how they short-cut the start-up process in ways that allowed them to build as they grew.
Absolutely! Start building your own things as soon as you’re comfortable. You can keep your progress organized by building some scheduling into your planning (either through something like Trello, the Github project tab, or just plain lists). Break it up into chunks that make sense and don’t get frustrated when you need to change it. Just update and keep moving.
Yup. There’s always going to be pushback for the same reasons as above. People want you to have that top-dollar future. Don’t worry too much about it. When they bring it up, thank them for caring (which they do… and people caring about you is a wonderful thing) and gently tell them that while you might not have all the answers, this is a passion and you’re going to chase it down.
The big question with no straight answer.
If you can see the future in your friend’s site, I say go for it. Just a warning… I’ve helped friends with their side projects a few times and haven’t hit one yet that was “minimal”. Scope creep happens, so expect to have hard “this should wait until version 2” talks.
Or bootstrap (not the library, but the process) and short-cut where possible… you mentioned that this was supposed to be a prototype, so keep “eye candy” to a minimum and only focus on functionality. Use prebuilt tools (Wordpress, Codeigniter, and others if it must be PHP. Node, Express, React, if it can be JS) and the skills you already have for quick turnaround.
If you can’t see the future in your friend’s site, you have even harder decisions ahead. I’ve had to walk away from friend’s projects too, because I didn’t feel like it was a solid use of my time. Remember that every time you agree to do something, by proxy you’re also agreeing to not do other things (like spend time with family and friends or pursuing your own dreams). Time is fixed, so use it wisely.
Hope this helps.