1. As long as you got a complete hydro-tappet head you'll be fine (the camshafts are different)
2. Ask 'HÄR!ߨ' about the exhaust manifold tool as he just bought one.
OR do what I did and make your own using a large exhaust 'U' clamp, swap the clampy bits outside the 2 nuts, slip it inside the clips and loosen the bolts till you can lever it off:

3. Halfords sell a set of splined bits for your head bolts, do what I did and take a bolt with you and then find the tool to match

Oh and if I were you, I'd consider getting a manifold & downpipe from a later MK2 GTI with the 6 bolt connection, the early 'toilet bowl' setup doesn't seal as well! I'd then assemble the head with both manifolds & downpipe together on your workbench then with the help of a mate slide it onto the car complete, makes the job much easier!