I really like the Egyptian klickies and chariot. It sounds like you've got your army off to a good start with 20 men and two chariots and have a good plan, da Hugh.
I think 20 soldiers per unit is a good number as it looks very formidable yet isn't overwhelmingly large to move. My Roman centuries have 20 soldiers each and the 1:4 play to historical ratio works well. I was originally going to have my Egyptian units be 20 soldiers as well, but I then decided on larger units, as the Egyptians were organized in companies of 250 men each with a battalion consisting 500 men with one company of heavy infantry and one company of archers. To maintain my 1:4 play to historical ratio would have required companies of about 60 men, but I felt that was too large, so I settled on 40.
With the five-man packs I've created 40 heavy infantry (green accented breastplates, helmets, shields, and spears), 40 heavy cavalry (blue accented breastplates, helmets, shields, and long spears), 40 light infantry (barefooted men with red accented shoulder armor, headbands, and axes), and 40 archers (green accented shoulder armor and cloth headpieces). I've made the blue backed red accented breastplate klickies my standard bearers and trumpeters and have created a custom officer, armed with a khopesh, for each unit. I'll try to post some pictures eventually.
I didn't get all these sets at once, although I did complete my purchases within a three-month period. Ridge Road Station's 15% off coupons, free shipping, and no sales tax helped ease the pain a lot. I've told my wife I'm finished buying Playmobil for the most part, as I'm running out of room, but if they re-introduce a new Western theme, I'll probably be there, much to her chagrin!