About the classes:
A little clarification
Marksman: The marksman isn't a sniper, think him more so as a sharpshooter in RnL or a marksman in RO2 with the Gewehr 41 scoped.
The scope will be very difficult to use, it'll only allow a small viewport with which to "pick off" enemies of importance. The pistol is there as a just in case option - as "high importance" troops were often granted a side arm.
The bomber, upon reading a lot of WW1 memoirs, bombers were often the strongest men from the battalion, issued with a good few grenades (and sometimes a pistol). The job of this class will be to clear enemy trenches - providing support for the infantry... but the two classes go hand in hand with each other. Bomber helps inf, inf helps bomber...
The machine gun crew member, again is based on historical accounts. The last British veteran Harry Patch was part of a lewis gun team, he recalled often how vital the team was behind the gunner. The team had someone who could repair the lewis gun, someone who could help with reloading and several members who could carry extra ammunition and help guard the gunner. The machine-gun crew member will kind of be tasked with protecting and both assisting the gunner.
Of course, each class isn't final we'll be doing a lot of testing behind each.