Hi, and well done on buying a fine car :D
No need to change the head gasket unless you've got a problem with it or you're taking the head off, as it is already of the metal type.
Strengthened cambelts are a bit of waste of money aswell IMHO.
If you want more boost, you need to decat fully, colder plugs and change the fuel pump, and go to a max of 1.2Bar
You already have a dump valve, so no need to go aftermarket unless it's not holding, or you want a dump to atmosphere one.
You also already have an intercooler, which is a side mount, you could go for a front mount, but for the expense at this level tune, the benefits are negligible.
Do a Google search for aristo boost and see what that brings up.