I launch from beaches with small protrusions all the time. It really depends on the type of protrusions. If it is weeds that bend pretty easily or grass, the protrusions are actually helpful as then you don't have to weight the trailing edge in light to moderate winds. However, if the protrusions are woody of sharp, then the tarp is a good idea.
I do think the water launch is totally feasible. Make sure you loosely roll the ends to the middle before you head out and make sure the butt port is CLOSED! It may be tricky the fist couple of times, but it does work like a charm. Just don't try it in super light winds. You need decent wind to inflate the kite when it is sitting on the water.
Water setup/launch and land/pack down. Much easier than you would imagine. You'll damage your kite launching on rocks like that. You only need to preinflate on the water enough so the vent area has enough inflation so the vents will work and catch some air, i,e, not much. Foils are quite tame till they get some air in them and even then they dont deathloop etc. Pull any line in and they will flag out. People often get scared of them because they see them do the weird stuff they do like windmill, tangle up etc and think in terms of if an inflatable did that it would probably nearly kill them.