How do I insulate my steel garden shed/office?

I am building a 7m x 3.5m garden shed/office using a steeltech type vender.

Originally A1 sheds recommended 50mm Kingspan for walls and pitched roof but I want to insulate this office once and make sure it's done right.

This building will be used as an office, play area, pool table, tv room whatever so I want the insulation to be top notch.

Some sites recommend spray insulation, others warn against. Some say the floor needs to be insulated too.
I was thinking 100mm Kingspan for walls /roof and then slab over it and skim plaster for a nice finish.

Can anyone recommend a method they used in a similar scenario that they can vouch for? .i.e no condensation or damage to items being stored. Good u values etc

Totally out of my depth here so appreciate any advice.