It is perhaps surprising that there appear to be so few 20mm napoleonic wargamers out there. 15mm and 25/28mm dominate the metal market but the advent of 20mm plastics to add to Airfix, from the likes of Revell, Italeri and Hat has given a much needed boost, to what in my opinion, is the "best" scale by far. 15mm allows for games on a small table but too often the detail on figures is lost while the requirement of space for 25mm/28mm means that you may well need a table of Arthurian proportions.
20mm or 1/72 has the best mix. 12 x 6 table is ideal but 8 x 6 should also be fine. As to the figures....New Line Designs do affordable infantry though the figures are the smaller 20mm. Their cavalry is disappointing with lame looking horses that are simply too small. SHQ are more expensive but if you want la creme de la creme you may well need to look abroad.
Art Miniaturen in Germany have a range of excellent poses and this is where to get your cavalry. Not cheap by any means. A regiment of cavalry (16 figures) will set you back at least £35 before any shipping/postage is taken into account. Once painted, however, their static poses especially look excellent.