oregonshooter,
1. Go to Wayne Lagger's site @ LPS Tactical (lagger-pro.com), and look up the parts under "Universal Housings and Options". There will be a picture of the M14 and M16 mounts in the left hand column. I prefer the M14 mount because it has a little more purchase area on the barrel than the M16 mount. These are the barrel mounts. Underneath the pictures will be a list of all of the mounts, and in this list, you will find the M31 "high" mount that goes on the flashlight itself. Mine M31s stay on my M3s permanently and still allow the lights to be used as a hand light without too much trouble. Surefire will have a picture of the completed assembly on their website under "weaponlights/rifle and carbines/classical mounts", but I think you are right - they will not have part numbers. I just buy all of my parts from Wayne and Micky at LPS Tactical. SFM14, SFM16, and SFM31 are the formal part numbers (for "Surefire Mount") but Wayne Lagger justs list them as the "M14, M16, M31" on his website. He knows what you mean once you explain it to him. IT DAWNS ON ME THAT THERE ARE PROBABLY SPECIAL MOUNTS JUST FOR THE AK47 IN ONE OF THE OTHER COLUMNS. IF SO, WE ARE INTO "PLAN B" POSSIBILITIES. Sorry, I think in solutions for AR-15 only.
2. I would VERY MUCH advise against the M4 for the following reasons. The M4 was developed, I believe, to be a high-power, long-range, sniper light, and in this role it performs very well. Unfortunately, it doesn't do anything else. It is too long to carry in anything, too heavy to move over distance, too heavy to swing when mounted on a weapon, too limited in function and purpose, and a pain-in-the-*** in general. If you only have to move a short distance, or function from a barricaded position, this might be an option.
The reason that I recommended the M3 is because of the versatility. In 60 seconds, it can become an M4 by screwing on a Surefire A-19 battery extension, or a "lighthound.com" MC123, hard-anodized battery extension, using the KT-4 turbohead and then choosing your bulb for performance - The MN-60 for 225 lumens for 1 hour, the MN-61 for 350 lumens for 20 minutes, or the N-62 for 500 lumens for 3 minutes (and M6 performance before thermal shutdown for 3-4 minutes for battery cooling). This is all in addition to the other M3 configurations and capabilities: M3 with regular head and the MN-10 or MN-11 bulbs, M3 with KT-4 turbohead and the MN-15 or MN-16 bulbs, M3 with the KL-2 (for 15 hours of runtime) or the KL-6 for 90 minutes of runtime in a great, shockproof shotgun light. I run all of my M3s with a regular head and high-power MN-11 bulb all the time for size, weight, ease of carry. I can always "configure up" for dedicated throw or whatever as needed. I just "creep" a little closer, that's all.
The SFM14/SFM31 mount combination WILL clear the barrel (in a turbohead configuration) by about 3/16 of an inch or so, but you will NOT be able to get a filter cover on this configuration. It will not clear the barrel without modification and if you DO modify the filter cover, you will incur heat damage with subsequent firing. This is one reason that I always use the regular M3 head. It lets me "filter up" with any option, as well as give me minimum weight and size.
The M3 DOES have a 1" tube for mounting purposes. I am not sure what a QD scope tube to a 1913 rail on the forend grip will look like or how it would function, so I cannot recommend anything there. I tend to be prejudiced towards simplicity, quick-disconnect, light weight, and ease-of-carry and operation. I absolutely would NOT go "dedicated function" with a permanent configuration. I feel that this limits the use of the weapon too much. I have to carry this thing 14 hours a day and I can tolerate the addition of 1 oz. of weight in a barrel mount for a simple quick-disconnect and a foolproof operation by pushing against a tailcap. Anything more begins to tax my sense of humor. Sorry, philosophical hardening-of-the-arteries.
3. Nobody competes with Surefire for dedicated weaponlights or mounts. This is their "raison d'etre". Everyone else is a pretender.
4. Sorry. After I posted this, I realized that I forgot to address your holster problem. Apparently, "John" from the former "SOEgear.com" separated and went his own way. He is supposedly building his own website to sell holsters but is not yet organized. Some people have reported a problem getting in touch with him. I have not tried. I have 30-40 of their holsters and some are great, others needed re-design. Their M6 holster is great! This is the holster that you need for the M3, no matter what confuguration the light is in. This holster will fit all configurations of the M3 or M6 (BUT NOT THE M4 - IT IS TOO LONG!!!). If you cannot get this holster, the "Blackhawk M6 holster" should be a nearly identical option in both form and function.
Hope this helps.