I've just re-acquired a copy of the Quarrie/Airfix/Napoleonic Rules In terms of British fire factors, Quarrie rates Fusilier Regiments on a higher factor than Line Infantry and on a par with Grenadier Companies and Light Infantry. When it comes to Mellee he rates them better than Line, Grenadier or ...

I use 2mm MDF ones from ERM for 15mm figures. I'd be wary of 1.5mm especially if I was using 25s/28s. I don't think 3mm would be a problem, except you need to think how you deal with the edge. (but on 3mm there may be enough depth to have clear marks of colour as unit markers/identifiers at the rear)

I'm quite struck on the way Might of Arms works.

DBx basing. Seems to work well for classical "ancient" as well as medieval

I'm just starting to build up armies for this using 10mm. I'm basing for Principles of War, i.e. Notional Units of 3 x 30mm bases each with 7 figures in ranks of 3 and 4 or 4 and 3 to allow "interweaving" on weapons protruding forwards. The same bases would be near enough to the 40mm DBx norm needed...