1000 percent LLC. I only say a truck mount because it's all there and you don't have to pay the extra insurance on the trailer. If you need a personal and commercial vehicle insurance goes WAY up and you need that trailer.
This industry is very saturated. Actually ALL property maintenance is.
That's awesome your helping him out. I would skip the college and invest in extra equipment/advertising. That's just my .02 cents but I feel hands on is the only way.
It sounds horrible but id say if your the only investor to let go of the other guy.
help out your kid but there's NOT going to be a profit to split the first year. Use him as a hired hand if you get a decent lot and need help. Keep at it and lay down good work you'll get businesses going sooner or later.