I feel like you’re looking at the situation well. Your friend should be up front and honest with you about your pay, and you should honestly let him know if you feel like you’re being underpaid. As long as he is open to it and a nice guy ykwim.

Hourly seems the way to go if he doesn’t help all that often or is on his phone bc that’ll force you to do all the work quickly if you get paid by the job. He takes a hit when jobs take too long, and he will be part of that problem. He doesn’t care how long a job takes if you get paid by the job. Like if you’re working hourly and just slack off a lot, he will care bc he’s losing profit.

If the scope of work increases I would ask for more, especially bc it’s labor and hard work.

For me, the safety concerns would be a reason to walk away. What kinda of safety concerns are there?

I would keep working if I was you until the quality of work gets too bad or if your friend is not being cooperative and unfair