I still have a 35 in my attic, haven't used it in years - there should be a diagram on the inside of the sliding cover for the condenser case, do you have that?
Couple notes - if your enlarger uses the 75 watt opal bulb that looks like sort-of-a-regular light bulb but a bit narrower, you don't need the 35mm condenser - it was only needed on the original 35's that used a smaller bulb. You could always do a quick test and see.
The condensers go in where the curved sides face each other. Heat absorbing glass shows up on eBay from time to time, though you may not need it unless you're having trouble with negs popping out of flatness. Find an exploded diagram and google the part number, you may find one from one of the remaining enlarger suppliers.
You can make a filter holder from black cardboard - the filters don't really need to "clip" in and I tore the clip thing out of my holder, it was a pain. Just something the filters can rest on to slide in and out works fine.
That said, it's a decent enlarger to get started but very limited and flimsy (if you do things like split-filter printing, ghetto up some sort of brace for the top that attaches to the wall or ceiling, that'll help keep it stable). If you want to go 6x6 or 6x7 someday, there is a (pretty rare) 6x7 conversion kit for it, but I think that's a waste of money. If you ever want to upgrade, keep an eye out for a 67c. They're reasonably sized (vs. the 23c, so they ship affordable) and very stable, and show up on eBay often. They have some alignment capability (unlike the 35) and you can easily do 16x20 prints with them (I made a simple plywood box-type thing and braced the top of the column to my ceiling for big prints). I did take two lens boards and an old mouse pad and made a DIY "Besalign" lens board for mine when I had it, and I got perfect corner-to-corner sharpness on up to 30" prints. (I have an MXT now and passed the 67c along to a friend's daughter).
Best thing in your case - the 35 lens boards and neg carriers work with the 67, same parts, so you can eventually move right up to the 67, maybe even keep the 35 handy for flashing paper and so on.
Since your getting started with this, here's my favorite "next piece of gear" tip - keep an eye out for an audible repeating timer. The kind that "beeps" every second and you don't have to twirl a knob back every time you print. I found that being able to count out seconds for dodging and burning really helped my work. I also opened mine up and wired a 1/4" guitar jack to the switch, and got a musician's momentary footswitch ($15 or so) to plug into it. The footswitch is just killer for complicated dodging or burning, you have your hands ready and go rather than punching the timer and grabbing your tools.
