Petra, I there specific ones made for each model, mine is specifically labelled as "Reducer corrector -0.85x for ED80". You will need
this one for the ED102.
Not sure if your T adapter is suitable, there is also a special camera adapter with a wider throat (not all T adapters are the same) that is designed for Full Frame (talk to one of the many Michaels at Bintel, they should know, ask about the T adapter for Full Frame).
Nothing else should be needed, no extensions are necessary with the reducer, provided you have the stock focuser,
I had an aftermarket focuser but ended up buying another stock 10:1 because I couldn't adapt the aftermarket drawtube to the SW reducer.
I haven't actually fired a shot in anger with mine yet, but I can't see any vignetting and focus no problem on terrestrial tests.
I've uploaded some pics, first is the reducer and 5DII attached to the standard focuser, second is the part you remove, the third and fourth are to show just how wide the adapter is (the wide one is to the left).