Using lead... start with small batches.
You must check to see if the load agrees with your pistol with no lead fouling.
Too much powder, and you can get leading... to little, same thing.
The 45 might be a little easier to develop a good lead load, but I wouldn't use that as a deciding factor. There are good loads available in manuals or online you can use as a starting point to develope your own loads.
FMJ is easier to load, from just a mechanical assembly standpoint. Its usually recommended to learn reloading with FMJ, then switching to lead.