I don't see where anyone directly addressed the issue of the size of the condenser. The old DII had four different condensers depending on what size lens/negative you were using (I have a DII). The 3 1/2" diameter condenser is for 35mm negatives. For 6x6 negatives, you will need at least the 4 1/2" condenser; the D2's had a 4 13/16" condenser which took the place of the 4 1/2" and 5 1/2" condensers. There is also a 6 1/2" condenser for 4x5 negatives.
For lenses, don't forget to look at the darkroom classifieds right here on APUG. As far as lens boards, the flat board works for lenses up to 90mm and there are a lot of used ones out there. I don't know if I have an extra board for my extra 75mm or not.
Good luck with the DII. It's a 50+ year old enlarger that's almost indestructable.