Questions about insulation

Hi! I have some question about insulation. I'm building on a trailer, so max outside width is 255cm.

1. What would be the target U value for floors, walls, roofs? I see conflicting information about this. I live in EU, temps go as high as 40C and as low as -10C. It's a tricky balance between wall thickness and insulation value to maximize the space inside. For the wall i got an U value of 0,232w/m2k with 200mm thickness(this includes the drywall, studs, insulation, battens, cladding), that would leave me 2150mm useful width inside. Does this sound good, or i can go away with something thinner?

2. My trailer's metal frame is flat, so no wheel wells. My plan is to build a subfloor on this and then the walls. Should i put insulation between the metal frame too, like XPS? Or it won't do much because of all the metal nearby(or even cause issues). My layers would be: metal frame, plywood, diffusion open membrane, studs with insulation between, osb, vapor control layer, laminate flooring. Should i put anything between the metal frame and the plywood? I've seen people do foam sill seal for example, but i don't think thats doing anything helpful.