Floor and Wall advice

This forum is great and I'm learning a lot. I'm building a Benroy-ish design and wanted some advice
. I have a 5' x 8' frame and I understand that I have to get twice as much wood since they come in 4x8 pieces, at least for my floors that is. Weight is being considered tremendously. I'm going to an actual lumber yard, not the big box one we don't mention. I don't want to over build, which is a concern on here, but I also don't want to be sleeping on the ground because I went through my floors during the night lol. These are my questions, for now at least:
(1) For my floors, I was thinking of, from bottom to top, 1/4" ply ACX, 1"x2" skeleton (flat-don't know the material yet) filled with EPS insulation in the voids, 1/2" Birch ply on top of that for sleeping on. The bottom ply, the one touching the frame, will stick out side ways by 1/2" on the left and ride side for my walls to rest on. Should I switch the 1/2" ply from the top to the bottom? or it doesn't matter? I've read some of you guys do 1/4" top and bottom, even 1/8. I haven't read of any particular order that we should follow, meaning thicker wood on top or bottom etc...unless I missed it.
As for bolting, I'm thinking of carriage bolts or elevator bolts. For the carriage bolts, do I have to counter sink the bolts? won't it take some of the material away from the floor since its either 1/2" or 1/4" depending on which I have on top? will it cause problems with wood strength? I have read some mention it on here.
(2) My walls, will be 1/2" Premcore Plus White Birch (its lightweight) and I will cut out voids for insulation, 1/4 White Birch outer, and 1/8 or 1/4 Birch inner. TBH, I'm still working on the type of wood for the outer/inner skin. I'm attaching the walls with deck screws to the 1"x2" skeleton frame of the floor.
Any thoughts? I welcome any advice, concerns, tidbits, or whatever you have to say lol.

(1) For my floors, I was thinking of, from bottom to top, 1/4" ply ACX, 1"x2" skeleton (flat-don't know the material yet) filled with EPS insulation in the voids, 1/2" Birch ply on top of that for sleeping on. The bottom ply, the one touching the frame, will stick out side ways by 1/2" on the left and ride side for my walls to rest on. Should I switch the 1/2" ply from the top to the bottom? or it doesn't matter? I've read some of you guys do 1/4" top and bottom, even 1/8. I haven't read of any particular order that we should follow, meaning thicker wood on top or bottom etc...unless I missed it.
As for bolting, I'm thinking of carriage bolts or elevator bolts. For the carriage bolts, do I have to counter sink the bolts? won't it take some of the material away from the floor since its either 1/2" or 1/4" depending on which I have on top? will it cause problems with wood strength? I have read some mention it on here.
(2) My walls, will be 1/2" Premcore Plus White Birch (its lightweight) and I will cut out voids for insulation, 1/4 White Birch outer, and 1/8 or 1/4 Birch inner. TBH, I'm still working on the type of wood for the outer/inner skin. I'm attaching the walls with deck screws to the 1"x2" skeleton frame of the floor.
Any thoughts? I welcome any advice, concerns, tidbits, or whatever you have to say lol.
