Hello. Second time posting on the forum!
I've only started with film photography and I'm thinking about buying a japanese Nikon Nikomat SLR camera (it is not a Nikkormat!). I have a few questions though: first and foremost, will it be compatible with the more modern analog Nikon lenses I already have here?
Yes, the lens will be compatible as long as it has an aperture ring. The "G" series autofocus lenses are NOT compatible: they don't have an aperture ring.
The meter will "couple" with the camera, making metering easier, if you use a lens with the "rabbit ear", which is an "aperture coupling prong". Pre-AI, AI, and AI-S lenses have such a prong. Some a***oles remove them from classic nikkor lenses, beware.
Also, I heard somewhere that the light meter uses a kind of battery that is not in production anymore. Is it worth it anyway?
You can place there a #675 hearing-aid cell and it will work just fine. Just make some sort of jig with cardboard or whatever, so the cell stays in place, centered, and in contact with the battery compartment terminals. This is true for the FT, and FTN cameras. The FT2 and FT3, as noted, use a SR44 silver oxide cell.
The ones I really wanted were a Nikon FM-2 or F2/F3 but they are way too expensive for me right now. I could also try other brands, but I already have a lot of Nikon lenses and adapters here so it does not seem worth it.
FM2 is overrated and I find your camera much better built and more reliable.
I also thought about buying a Nikon F-601, but it appears to be very plastic-y and I don't really trust the durability (reliability?) of the electronic parts. I also saw a review saying it does not work very well with manual focus lenses, is it true?
It will probably be less convenient to use with manual focus lenses.