Usually I'm not usually one for banning bits of kit but in this case that's probably the best option, especially with how cheap and easily available they are from china with stated power ratings which are as accurate and believable as your horoscope
Then I suggest taking another look at how this is done as it's not working. For example you have an Elcan Specter scope with red dot listed as £300 best price from DCA, but 10 seconds on Google shows them going for the over £100 less and in stock elsewhere. This sort of thing doesn't instill...
Another problem is the levels of QC in airsoft. You could take two "identical" items from the same factory and one fits ok whilst the other needs to be butchered with a Dremel
After an admittedly brief look I don't think I'll be signing up. There's rifs listed in completely wrong sections and some of those best prices are worthy of Mack's
Tbh I wouldn't get too hung up on doing a perfect paint job. 99% of people won't notice and in my experience the rougher paint jobs tend to work a little better anyway
How to adjust the hop up should be covered for n the manual.
Muzzle energy for gbb guns changes with temperature so yes you might need to tweak your hop setting depending on air temperature.