Shed strip foundations, DPC and vermin protection...

I'm in the process of building a 2.7m x 1.8m timber shed in the garden. The floor of the shed is made from a 2"x4" treated timber frame followed by a damp proof membrane and then topped with 18mm Ply.

For the base I was planning on having 3 concrete strip foundations (one every 1.3m or so along the 2.7m length). These would then be topped with a row of engineering bricks and them some DPM between these as the frame. Does this sound ok?

I was planning on adding polystyrene insulation in between the floor joists below the DPM held in with timber battens in case I decided to insulate the rest of the shed at a later date. Is this acceptable or will it cause more problems than its worth?

I'm assuming the gap the engineering bricks will provide will give good ventilation but what would need to be done to stop vermin setting up home underneath?

If the structure will be raised on the bricks, then the polystyrene exposed to the elements underneath the floor, will be ok. There will be no vermin unless you leave gaps for them to get in, or regularly eat your sandwiches in there and forget to sweep up your crumbs.

TBH, for the size, you could do away with concrete and simply lay down some el cheapo paving slabs on a layer of tamped sand, then lay a grid of concrete blocks, spaced 600mm in each direction. Then simply sit the shed on these.