A Canon P is not compatible with some wides e.g. J12 and Kobalux 28mms they can interfere with the light baffles, some people use force. The 28mm Orion should be ok.
The FSU LTM lenses can be very good if you get one that has not been mistreated.
A Nikon f/2 in LTM is very good but very expensive.
A Canon LTM /2.8 or /1.8 also very good but both can fog and be etched if they have been neglected.
There is the Cosina Voightlander /2.5 if you can find one modern glass and multi coating.
There are other LTM lenses but all the LTMs have been inflating in price.
A Canon P can tolerate work Id not bother with a CLA until it breaks a ribbon or you get shutter taper.