It's hard to answer your questions without a visit.
Ask friends and family for details of recommended installers and invite them to quote.
Personally I wouldn't entertain installing a boiler that I hadn't supplied. When (sorry, not if in the lifetime of a boiler) it goes wrong, you would...
Sounds like you are describing a compound bow. They work on a cam system meaning that at a given draw point the pressure eases to approx 20% of the draw weight. (You still have to pull through the full draw weight to get there though).
No, no restrictions in place
As with everything there have been improvements in materials meaning, bows shoot faster, arrows are stiffer and lighter but the basic technique is basically the same.
What a load of ******. My open ended spanners rarely come out of the tool bag. A selection of Bhaco adjustables every time.
Guess I'm a bodger then, but can you explain why?!