On batteries, C rating means jack squat. Internal resistance is the spec that actually determines how many amps you can draw (both the absolute limit and the relationship between amp draw and heat production), but good luck getting a manufacturer to release that information. Your problem last year was likely due to a bad connection or just missing the setup with your motor and prop combination.

On airfoils, I don't know enough to recommend specific ones, but in general flat bottoms and even undercambered ones are going to give you the most lift for the least speed. So you probably don't need to bother with anything that is convex on the bottom. As you probably know from your studies, sharp leading edges and high lift designs will make the best use of your thrust, but also will stall quickly leaving an inexperienced pilot little opportunity to recover. So consider the actual flying conditions and pilot workload when making your choice.