Dont worry too much about the freezer, I never had problems with any valve freezing.
Yr missing the bleeding thingie though, cant see it on yr pics.
Filling is easy, screw it on (I advise gloves) and screw open the valve. Doesnt have to be slowly, its not pcp, it fills on weight.
If its slightly overfilled, you get first shots louder than usual. But dont really overfill. It wont shoot well.
I had mine converted because it needed an overhaul and pcp conversion was the cheapest option, but it does 70 shots tops on pcp..
Its empty before you know it with the 5shot mag..
While the morini pcp etc easily do 200 shots on a fill..
Also have issues filling; when I screw it on the bottle to top up, it totally empties.. Kinda worthless..
You cán convert it, but imo, its not really designed for it.
I think 250 is too low, LP5's are rare, and are worth more than LP1's.
I'd keep it on co2.
Only downside is, that it may freeze up when really fastfired and co2 is low.
And ofcourse, balance change.