Here are a few basic experiments with basing, and my initial thoughts. I've taken some of the Airfix figures to try with this, as they seem to have the greatest variance in base-size. Plus, it also lets me take a break from posting endless lists of boxes, and put some pictures up for a change!
I am basically sticking with the 'Horse, Foot & Guns' ruleset for basing, and I have plumped for a 60mm frontage. A single Base-width in HFG is scaled as about 300 metres in the 'real world', so this means a manageable tabletop distance of slightly over a foot (32cm) being equivalent to a mile (roughly 1600m.) Nice! It also proves handy as a decent size to fit 4 horsemen onto a base, which is a nice number - 3 looks too sparse, while 5 is a bit of a crush!
The above pic is of some of the French Heavy Cavalry, and I've used some spare bits of card to frame-out a base 6cm wide by 4.5cm deep - keeping base-depth in scale with width, as per the usual DBA norms. Airfux cavalry seem to have unusually big bases, like a big splodge of chewing-gum. I may have to clip a few when I glue them down to a base, but overall, the riders themselves look decently spaced out.
Next up, some artillery. These fit very nicely onto a 6cm by 6cm square base, giving room for a single cannon and a crew to stand around it without looking too cramped for room. With these two, the next question was about Infantry - could I get 8 or 10 figures to a base?
The answer, it turns out, is ten - even with the random footprints of Airfix. This base is 6cm by 3cm in size, which takes a nice double-rank of ten figures, two ranks of five. Airfix also seem to have no real uniformity in poses in a figure set - others appear to standardise a lot more but I've been certain from the word go that I'd need to have mixed poses on a base, so it's not a problem!
Relating to the difference between 8-figure and 10-figure bases, or even the possible double-base option in future for Black Powder, I think I'm safe plumping for 10 figures a base as the cost difference is negligible and availability of infantry boxes appears good. Plus, frankly, I think it looks good!