I would prefer a more substantial frame 4 brackets screwed to the roof and dicor'ed. Mine haven't moved or leaked.
100w panel weighs 20-30lbs. Not even enough to worry about. They don't flap in the wind can be tilted or removed if you desire with the proper brackets. Don't reinvent the wheel :) look at a few installs and just mount them.
400 watts should do what you want easily .. besides the panels you also need a controller. Your gas refer shouldn't run via the inverter unless you wired it differently gas refers use more energy on electric than a residential.