I'd wait on the Ruger SR9. The first ones had a recall on them and maybe it's been fixed by now, but I'm always hesitant picking up newer guns. My buddy has a P345 and I don't care for it. The trigger feel is horrible IMO. There is too much movement in it. I prefer my Springfield XD over it and my XD holds more rounds even in the compact mag (10) and the Service mag holds 13. Unfortunately no .22 conversions for the Ruger or XD.
If you want to stick with .45ACP, then definitely go with a 1911. They have 7 or 8 round mags and numerous companies make .22 conversion kits. You can practice the trigger pull of your gun, with the low cost .22s. If you like the feel of 1911s, try out a Ruger 22/45. They have the same grip characteristics as a 1911 and all the controls are in the same place. Trigger pull is different though.