Rob i think the only way you you will find out is by the good old trial and error unfortunately. I was in the same boat and mine looks as though it will work out in the end.

As for your questions..

How much you shorten the tube by will be determined on what length inserts you get, the shorter the insert the more you shorten it etc.

When fitting the sleeve kit (which is the same as mine) get your shortened strut and put it all together without welding the sleeve on, have the adjusting nuts at the top and put the 2 helper springs in.. once its all together tack the sleeve on. Disassemble and weld it up! this will place them at there highest point (which will be now lower then stock) and you have the option of winding the front down with the nuts which is around 4" from memory, and can also remove the helper springs which will lower it a further 2".. or one or the other, or both lol.

Dont wanna weld them too low to start with or it may result in stuff all travel.

As for the spacers, i cant help you there.

And the inserts, mine are 200b struts and i used R31 munroe inserts, which were a fair bit shorter.