What size should i use for my intake tubes? Is Sch. 5 too thin?

Schedule 10 is about the same wall thickness as good exhaust tubing (16 guage). Just remember when you go to get your connectors, schedule 10 is PIPE, not tubing. Pipe is measured by Inside diameter, and tubing is OD. Silicone hose connectors used for air intakes are for tubing. Pipe is for plumbers and poop. Use exhaust tubing, mandrel bends are easy to find and the connectors will fit.

Wall thickness changes with pipe diameter. FWIW, for most of the useful size ranges you’ll sch 10 will be about 2x the thickness of some 16ga exhaust tubing.