As a base rule I usually go for 4 mechs for 1 map.
That is what is suggested in TW so you are right on there.
I was wondering what reasoning you guys use to determine the number of maps you use?
I start with the TW recommendation of 1 per 4. That of course is assuming a pair of medium/heavy mechs/tanks.
I will modify that figure based on tech, terrain, and even units involved.
1. For a Clan or IS L2 tech I normally add another map in 1 or 2 directions. (Turning 1x2 into 2x2 or 1x3 or a 2x2 into 2x3 or 3x3)
2. For a pancake map you might want more maps to run around, but, if your playing on mostly forests & hills then you don't need 6+ maps, because most combat in that terrain will end up at close range anyway.
3. Units involved can also change things, an assault slugfest won't use up a lot of space flanking, nor will an urban battle of Demolishers & Infantry.
That said, a pair of Mixed Companies going at it w/ Mechs, Vtols & Hovers might find even the base 6 maps to be restrictive to really get in good flanking maneuvers.
I would add that the single largest mapsheet I've ever used was 12 arranged 3 wide by 4 long, and that now days we rarely use maps but the felt mat we use is about 2 maps long by 1.5 maps wide IIRC.