Last I looked XD dont sell the barrels or conversion parts by them sleve .. There migth be after market companies that do this I have to look been a long time since I mess with XDs.. But for parts etc etc etc not a issue .. Getting spare parts more so but for normal stuff like mags /holter etc not a issue .. Due note there is a xdm and xd version so look and see what looks for you
Now for glock yes either putting a 40 cal barrel or a glock 40 cal slide on it will covnerted it .. Now I would not carry it as such unless you fully swap parts ... But for range etc not a big deal
Either gun will have plenty of basic aftermarket stuff night sights and all that so unless there is a certain type you need you should be able to find something ..
As for the safety personal call .. I wont weight on that .. Just shoot them both and see what you like is all I can say..