OK so rang Nizpro today to ask them a few q's.
1. The Ford ones are apparently pretty good, but replacing them if you can is a good idea. Turns out that Nizpro had already put some inconel locking nuts on my turbo, so I can re-use those. If you've got the stockers its a good idea to get something of the locking variety.
2. I think as per point 1 would be a fair conclusion. If they're hammered, change them
3. Nizpro def recommend a gasket between the turbo and manifold. The metal to metal fit doesn't last over time and will leak with expansion and contraction.
4. Still TBD
5. Still TBD although I borrowed a really long 10mm ring spanner from a mate. It would be twice the length of a stock spanner, should work OK.