Welcome to the forums. In order to get the most out of an XHP70, I would recommend 10 amps or more. The Taskled drivers are great, but they do not push a lot of amps. I would go with a FET driver from RMM - Mountain Electronics. It can run 2S with no problem and it can be run with a clicky or with a momentary. It can even be done with a regulator instead of a zener, so the momentary will not cause parasitic drain. Contact RMM here via PM on this. This is with the XHP70 running 6V. If you go 12V, then it would not work the same.
Definitely, you will need more heat sinking and/or better heat transfer out of the plastic body light. A finned heat sink is an idea, or a cooling fan, to help take heat out of the plastic housing. It will heat up so fast, you won't believe it. Fast enough to melt plastic before you blink twice.
Of course, you could make an aluminum head and body out of aluminum tubing and rod stock as well. I don't know if that kind of thing is available over there. It's easy to get in the US, but I don't know about international.
I would not dedome the led if using the LUM5-90 reflector, unless you want a very tight spot. The spot as is, will be very nice with the domed led in that reflector.
https://budgetlightforum.com/t/-/32603 gives some idea of the beam of that led and reflector.