1 piece or 2 pieces I have used them on the FM2, FM, FE, F3, F2 without any problem. There must be something wrong with the cap if that is the case. You can buy the 1 piece battery if you want.
I think you can skip the flash meter but a good used one for $50 is nice. For that type of shooting I agree you don't need iTTL or CLS. Just manual is simpler.
For long exposure and exposure on tripod I always use manual mode so the eye piece blind isn't needed. I do feel the Df without the finder blind is a cost saving I don't like.
My 60CT4 is nice because I can use it at ISO 1600 and f/5.6. At that setting even with bounce it will recycle very fast.
What would you want for your 45 with bad battery pack?
I don't generally use the manual mode on the flash with the flash mounted on the camera. I use it for a lighting setup with the flash on stand or tripod in which case I use my Metz 60-CT4 which has 27 steps manual power.
I manual focus with the 45-CT1, 60-CT2 and 60-CT4 without a problem. The 45 series although smaller is a bit heavier because it's self contained. On the 60 most of the weight is on your shoulder.
The 60CT4 is nice because I can use ISO1600 @ f/5.6. At that settings it can recycle very fast.