What I think is what do you mean by line because what I think of line is... Medics, machine gunners, Infantry, sapper and officers
Yeah, officers, medics, ammo crate guys, and regular infantry. Basically everything to be self-sufficient. With bleeding out a real thing to worry about in the mod, a medic or team of them right there with your guys is the best way to keep your line falling apart on you from people getting wounded. Also ammo goes by pretty quick when you're in the thick of fighting, so the ammo crate being ready for deployment is a great hub for your guys to restock on ammo (which isn't unlimited, mind!)
Not MG gunners; I think should have their own role to play separate from the line being so few in number. What I mean by that is if you have a MG per regiment at an event let's say... well, they'll be up there with their guys acting under the orders of the officer. But if you had the MG guys of the whole team working together as a regiment, you could coordinate intersecting fire and have the LMG teams plug the gaps or move quickly forward. Also sappers would be better used with the assault troops, IMO.