Wood types

I'm just about to start making my first dulcimer. I've previously made a mahogany ukulele from a StewMac kit and a Cajon from scratch. For the dulcimer I have decided to combine a fretboard from a Folkcraft Cardboard dulcimer that is currently in the mail while replacing the cardboard with something of my own construction. My goal was to build something nicer than one made from cardboard but not as expensive as the full hardwood kits I've found. Sound quality is secondary, if I can make it sound as good as the cardboard that's fine, If I can make it sound better that's a bonus.

I can't find any locally sourced solid woods for the back, sides, or top that are thinner than 1" and I don't have means to thin boards. I can get 1/8 Birch Plywood and might be able to get some tonewood from a local Luthier whom I found on Marketplace (if he has anything big enough because I think they mostly make guitars). I see two options: 1. build the bottom, sides, and top from 1/8 birch plywood. 2. build the bottom and sides from 1/8 birch plywood and try to get tonewood for the top. 

My questions: Will 1/8 plywood sound comparable or better than cardboard? Is there any point in making the top a solid tonewood if the sides are ply?

Thanks in advance and sorry if this has been asked before I couldn't find the question.