Sweet modification !

My son has the same gun and I was thinking of doing the same sort of thing to it only I was thinking of mounting the bottle to the gun somehow...

Will changing it over to HPA make it shoot faster or just give you way mor shots? I don't want to make it shoot faster because it's my 10 year old sons gun .....

I find the trigger real stiff on this gun ....is there a way to fix that ?