belt yes,
tensioner does eventually leak so a good idea.
pulleys only really if the bearings in them are going
water pump no need
avoid cheap copys, if one of them fails highly probable that's your engine gone with it
will need mapping for those mods
Looking at it its going to need some work, looks like both rear arches are going, when rust is visible means the inner wing will be a right mess so that will need doing as well. Prob looking at £300 ish per side.
need to find out about the service history and what is ment by 'full'.
my dads did a bit, they put this !Removed! protection gunk all over the engine and that tends to smell a bit, but as you say depends on what it pongs of