space marine weapons are a no no.
lmg - bolter NO, bolter only has a 16 round mag that is more power than the ns gl,
pistol - bolt pistol NO, once again only has 16 rounds.
hmg - heavy bolter - GOOD GOD NO, with a solid slug round the size of a gl nade any thing it hits will be ripped apart in 1 - 5 shots (yes even an onos)
gl - plasma maybe, but i dont think you could make it look right,
shottie - well a shottie oviously, i guess that would work
as for the light armour rine a scout would be the best put they cant use jps so......
and heavy would be a standard space marine cause well there 7ft tall and like 2 foot wide
(of course this is only true if u want total realism to the 40k universe)
if u really want stuff from 40k i suggest using the cadian guardsmen cause there just cream your pants sexy