Not Prissy at all mate. When you fork out your first months earnings on insurances etc to then hear its not complicated....go get yourself a ***** job for £100, let us know when you want it doing properly, after you've redecorated etc due to leaks.
The old type 1 and 2 underlays used to contain Asbestos. However, its encapsulated in bitumen, so unless you grind it up and snort it, of no real harm.
Go to car body supplies shop, get some seam sealer. Break and clean joint, insert sealer and bolt up. You can get a butyl strip to do the same, but seam sealer works perfectly.
Felt and lead detail is standard for a flat roof onto vertical tiling. Looks like they forgot to run the batten across the window, and I suspect the additional tiles are covering a hole up. To much cement in the mortar too which looks like it went in via catapult.