i think it should be looked at in a different way, not as a "practice" server but more as a fun little side server where u can have some down time, maybe even make it donator only to help w the costs!
pvp has ALWAYS been seen in a very negative light in the rp space and for good reason but when it comes to it, its fun! i can PROMISE you, if it gets added NO ONE is going on there for 7 hours to "practice their gmod pvp", we already have 1942 rp for that lol, there are also 100x more effective ways to "practice" if your that dedicated to mafia pvp. it will most likely be used for friendly 1v1s or 2v2s ect ect!
and at the end of the day, if u dont like the pvp dont join the pvp server! (if it gets added)
ps, if it does become a thing, i would imagine it would be like the old pvp system with 3rd person and no recoil as that is what that majority of pvp enjoyers would prefer so you wouldnt even be "training" functional skills that you could bring over to the live rp server