I'd recommend that you get AI lenses.
Nikon manual focus lenses are backwards-compatible, but not always forward compatible.
The FE and FM take AI lenses, and you can use AI lenses on your FTN, too.
If there are two sets of aperture numbers (one big set, one small set) on the aperture ring of the 24mm lens on the Nikkormat, it's AI.
IIRC, mounting non-AI lenses on your FE or FM will damage the camera's AI mechanism.
50mm f/2 is highly regarded, ubiquitous, and inexpensive.
50mm f/1.4 is also highly regarded. You're paying more for that extra f-stop...
The 50mm f/1.2 lens has attained cult status and price.