well, i agree they should more elaborate on bonuses/maluses pased from army/corps leader to subordinate leaders, how stats/traits are counted, but thats all.
and yes, explanation of minefileds and how they work - if they work at all - will be nice too.
all other problems are easy to solve by just thinking.
river monitors, with some history knowlenge is is extremly easy to solve, since in history monitors were combat ships which served on shore defence or rivers. so thier function in game is very easy - to patrol rivers/coast and fight enemy shipping if encoutered.
one can say, that by just looking at thier stats and comparing them to river tranports, will say - boot are river bound, so they have same rules to operate, but hey, looking at thieer stats is saying they have bigger combat value, so they will serve as thier escorts or to combat at rivers.
magazines/ammo dumps - lol, just hoower over thir picture, at it will say all, they store mainly ammo for artys with very low of supply amount, exactly oposite of normal supply train.
subs, yes, more elaboration on them will be very welcomed, but it seems they onlyest use for them is in merchant box , since they have very low combat value and well, so only useful for central powers there, so for entete is fully ok to use them in naval combat, but cant expect anything from them.
i looked at them carefuly, but it look that they lack any special trait (e.q. submersible), so while in reality they were deadly against any unescorted capital ship, here in game any unescorted capital ship will wipe they out due to combat strenght difference, and subs high evasion/hide dont help them in combat.
but yeah, subs only units can be useful for just spoting/scouting purposes since they have nice hide value.
if you have more questions, just post them there, this is what forums are for.