my tuppence worth.
Get the turbo fixed...bolt it on and go camping in it.
IF the rest of the engine is furbarred....at least you will have a good turbo to sell on....so it won't be money wasted. I don't do diesel...but have heard a properly running 1.6TD is economic (as much as anything wedge shaped is economic) and cruises nicely.
You haven't had it long...see if it suits before you go throwing thousands at it. Seems you have done the basics already to get it on the road. Summer is just round the corner (apparently lol) - use it, read up on the proposed engine change, accumulate all the bits and do the change over winter. Until then...enjoy the bus!!!
Em
xx
(oh - you will also have a engine with a bit of history to sell on for parts or as a runner

cos you will have driven it, or had a ride on a flat bed.....but at least you will know....)