My first classic 35mm SLR camera. Any suggestions?

I've been looking at either the Nikon F Photomic FTN or the Nikon FM2.

I know that the Pentax k1000 is a good beginner slr but I would like to be able to use the majority of my equipment when I upgrade in the future.

Depends on how classic you want it. The FM2 is a full decade later.

Buy a Pentax Spotmatic 1000 or F! Many are still in 100% GWO, the build quality caused some reviewers to suggest that Asahi were losing on each one sold and they are light and easy to use.
Screw fit lenses can be easily adapted to any dSLR except Nikon and the quality of the Takumar range still impresses. It was believed at the time that Asahi lense designers were trying to match the quality of Leica lenses - mine still feel silky smooth after 55 or more years.