Series two rules in hand

[Blackcloud6]

 

For my Vassal graphics I've been marking the artillery & mortars as platoon size, and the MGs sections. I think the MGs are generally platoon sized units, but in literature they are usually referred to as sections. Wagons I left as companies, though I think the unit size is indistinct. I see transport as not so much 12-15 wagons, but better defined as enough to do the job.

You might want to reconsider that.  First the symbol is correct to indicate a battery.  Second, and more importantly, a WWI Artillery battery was a good-sized unit in terms of personnel and footprint.  For example, "A wartime-strength German battery included six guns or howitzers, 5 OFF, 188 EM and 139 horses, the battery commander’s observation wagon, two supply wagons, a ration wagon and a wagon for fodder."  (From German Artillery 1914 | Weapons and Warfare).  Compared to a rifle company which was at a peacetime strength of 150 and up to 270 men after mobilization, which was likely never met. (Source: German Infantry Division 1914/18 - Visualization - Organization & Structure (militaryhistoryvisualized.com))