Can't advise on Holsters but ammo.....
If you got a "good" P11, and by the feedback on the KTOG forum, most of the newer ones are really good, here's what I've used in my P11: For carry it's CorBon 115 gr JHP + P. Now, mind you, Kel-Tec does not advise continuous shooting of + P ammo in their P11 but I don't think an occasional mag of this stuff would loosen your gun. Georga Arms also makes an excellent 115 gr JHP which is rated at approx 1,100 FPS, quite peppy for a standard pressure load. You can get a bag of 50 for about $8.50. I would also seriously look into RBCD ammo which is an exotic and labeled as "TFSP" which, I believe, stands for "totally fragmenting soft-point." I used this stuff in my P32 and the RBCD 9mm goes out at almost 2,000 FPS. Something to think about for a self-defense gun, which is what the P11 is designed for.