There is a 6x9cm glass carrier for the 23C, don’t believe any others were made.
Keep your eyes out on eBay for lenses, bargains appear regularly, and I’ve gotten most of my enlarging lenses via best offers decently below the asking price. They simply don’t move.
The 80 Nikkor is much better than the 75 in my experience with several examples of both while I taught in a place with a big lab. I’ve settled on Componon-S for most everything I print, all found at a tiny fraction of what they went for new. Patience is key.
Alignment with the Beselers can be a challenge. I would suggest rubber washers for the lens stage side to side adjustment, and be sure the nylon gears On the chassis are in perfect condition. The rebuild kit is a worthwhile investment if gears seem at all worn. Granted most of my experience with the 23C is with heavily used gang darkroom machines, but I have rebuilt about 20 of them over the 15 years I taught, and was the only one who would align them. Shims for the frame/baseboard connection can also help getting things dead on, the weak link on later machines is the lack of adjustment to the negative stage side to side, where a weld replaced a nut and bolt connection.
Alignment is slow to achieve sometimes, the laser alignment tool is a boon for this task.