Congratulations on the acquisition of your PT909 and Welcome to the Forum! Please be sure to post a Range Report and let us know how it shoots for you! ;D
As for leaving magazines loaded, this is currently a subject of some controversy here. I rotate my loaded magazines in my home defense pistol on a regular basis, every 2 months. You should get spare magazines, particularly if your pistol is used for home defense. If your PT909 is not being used as a Self/Home Defense handgun, store it with the Magazine(s) unloaded.
The PT909 will use PT92 Magazines and Grips. I recommend the 17 round PT92 Mec-Gar Magazines from CDNN Investments.
http://www.cdnninvestments.com/taurus.html
For replacement grips, simply call the Taurus Customer Service Desk and order them.
Happy and Safe Shooting! ;D :shooter: