So after much thought and knowing I was going to get it wrong (or at least knowing that 50% of the wargaming community would disagree), I decided to go with the following. This was influenced by several decisions I had already made.
First, I was going to go with 28 mm figures because I like to paint and that was the main reason I had started the hobby. I did, however, want to war-game and knowing that the figure size was a primary determinant of the table size needed, I was going to have to jam as many figures as possible on the smallest base that I could. It seemed that war-gamers with 28 mm figures had 20x16 foot tables and I was never going to be able to fit a table that size that in my attic, thus the drive to use as small a base as possible. The third factor was that I wanted to get the unit divisions done as soon as possible and had decided on a 1:50 figure ratio, I wanted to maneuver battalions and the Le Feu Sacre rules seemed the best for me. Finally the look of it was important to me, I did not want to have units in line that looked square on the terrain, so I decided on single rank basing. With this and at least 4 bases for each infantry unit, I could easily form and more importantly be seen to form line, column and square. Cleverly this allowed me in the future to change the figure ratio to 1:20 (General de Brigade rules set) by just doubling the number of bases and arraying them behind each other essentially to end up with a double ranked figures (A long way off I suspect).
Infantry Basing: I found that most infantry battalion units were going to be 10-16 figures, so to get a minimum of 4 bases it was obvious that I would have to fit 3 figures to each base. Simple experimentation revealed that the appropriate base was to be 40 x 20 mm. I had also decided to base light troops on the same sized base but in 2 figures rather then 3, thus being able to detach them as skirmishers. Command stands were a bit of a challenge, as I wanted to use mounted figures as the colonel in chief, and one can not fit a horse on a 20 mm deep stand, so I had to use a 40 x 40 mm stand, with the flag bearer and the musician on the same stand. So each British or Portuguese battalion ended up having 3-6 (depending on the size of the battalion) 40 x 20 mm bases with one 40 x 40 unit command stand. I did something slightly different with the French units, as I wanted their mounted colonel to represent a regiment rather then a battalion. Look at the orders of battles for French units and you see that unlike the British, 3-4 infantry battalions of the same regiment were grouped together. So the regimental colonel was represented by a single mounted figure on a 40 x 40 mm stand. The Chef de Batalion was represented on a 40 x 20 mm stand with the flagbearer and musician. Otherwise the French Infantry units were based exactly the same (the one basing requirement of all rule sets) as the British units on 40 x 20 mm stands (French units were more uniform in size so in most cases the a battalion was represented by 4 stands, with 3 figures on each stand aside from the elite companies like the voltiguers represented by 2 figures per 40 x 20 mm stands)
Cavalry Basing: Easy, 2 horses on each 40 x 40 mm stand, with the unit command figures integrated into the unit. Most cavalry regiments are made up of 4 stands in my army (400 men)
Artillery Basing: As much as I tried I could not get an artillery piece on a 40 x 40 mm stand with figures so I opted for 50 mm square stands with the number of figures representing the number of guns, i.e. each figure representing 2 guns. In most cases, each artillery battery has 6 guns. Most of my artillery units (batteries) are therefore on 50 x 50 mm bases, with 1 cannon and 3 artillerymen.
Command Basing: In the Le Feu Sacre ruleset, army, corps, division and in some cases brigade commander stands are critical. I used a pretty simple scheme:
Army commanders are 3 mounted figures on a round 50 mm in diameter stand (see Wellington and Massena above)
Corps commanders are 2 mounted figures on a 50 x 50 mm stand (see Loison above)
Divisional commanders are 1 mounted and 1 standing ADC on a 50 x 50 mm stand (see Crauford and Picton above)
Brigade commanders are 1 single mounted figure on a 50 x 50 mm stand (Beckwith is with his horse, try to find a mounted 95th rifles officer out there)