Hello and welcome!
I put a light on my .22 for dealing with late-night predators, first a Xenon incan and then an LED upgrade, and found some useful information. I’ll skip the mounts since you’re using your Service Weapon which probably has Picatinny Rails or some other mount already installed. Just get standard Scope Rings for your base. One or two will usually do (depending on recoil).
As for me, I found the Ultrafire 501b to be the best, since it’s just-about the lightest P60 host & uses standard P60 drop-ins. The notion of heat is valid, but IMNERHO on a weapon light you probably won’t leave it on long enough to get hot in the first place. If you leave it on too long, it becomes a target. Plus it’s hard to hold the remote switches that long.
As for remote switches, what I did was to buy a “complete” tailcap & remote switch, then took the switch part out & installed it in my own tailcap. That link will take you to eBay, which may or may not be available to you. Use needle-nose pliers or a small hemostat to disassemble/reassemble the endcaps. That’s assuming you can’t find one pre-made with a tailcap for your torch…
The implication of a Weapon Light is that you’re going to need illumination at a distance, which is called “throw”. None of the P60 hosts (no matter how well constructed) are going to “throw” light as far as your weapon’s effective range!! The best you can hope for is to buy an “optic” like one of these from Carlco (not an afflink, nor do I recommend them, just FYI) with a “Narrow” beam less than 15° to push as much light as you can downrange. OTOH, my neighbor has had nothing but praise for the C8 form factor. It uses essentially the same body (as far as the Mount is concerned) but has a much bigger head (you may need taller mounts) for a dramatic lot more “Throw”.
I can’t imagine why you’d want “zoom” on a weapon light, but I have no use for “zoomies” anyway, so I’m no help there at all.
As to batteries, and you already mentioned scrounging from “dead” packs, a good charger is more important than any particular battery, especially if you scrounge them from “high-end” (i.e. Dell, HP) packs. I can imagine a difference between batteries, but generally there’s not enough performance difference to worry much. Just visualize the proverbial bell-shaped curve & remember almost all the 18650s you’ll scrounge fall in that flat spot at the top. My best charger is a Miller ML-102, which requires a USB port or micro-USB cellphone charger, but you’d be better served by the advice of the others here re: chargers!!
If you’re interested in Modding, “buy the cheapest and replace the LED” is more expensive than you may think. It can work, but it takes a lot of engineering to pull it off. You are definitely in the Right Place for ongoing, extreme-level help/advice/education in that regard, but you’ll need to ask more questions to get more answers. I would recommend (for weapon-light throw) using an XP-G2 with the highest-current, single-mode driver you can find, just to get things started.
Hope this helps. I’m just
Dim