If you're not confident about your painting abilities...you could try something different.
First work out a way to get a 'basecoat' finish your are happy with (thats also speedy). Probably an airbrush/wash finish on your minis (the forum crowd here can probably come up with a way to this). Don't worry about any detailing, just cover the figure and get the tone you are happy with. On what paint to use, yup the foundation paints are good, but its going to be real expensive to cover that lot even with just one coat. Looking around for a cheaper airbrush friendly (foundation isn't that friendly) near match might be a good idea.
Then 'try' a few figures getting all the detailing on. If you are unhappy, or get frustraited...then you can seek the services of a professional painter to 'finish' these minis (it would be a lot cheaper that way). On the tanks/APC front, see if there are any 'model' societies in your area, these guys know how to weather armour VERY well....so you could get them to finish your armour.
Spraying is going to be hard as it looks like you have fully assembled all your infantry, so I'd suggest making a rack of a piece of wood with 10 nails/screws sticking out of one side with about 3" inbetween each. Then securely add half a wine cork to each screw to form a platform to 'blu tack' a mini and its base onto your spraying rack. Then its going to take a quick spray from front/below (as near as you can get), and rear below. Then frontabove and rear/above and finally front rear if needed. You can also look at washing the minis on the rack if your bluetack is good and the minis with stick around for this.
So look to experimenting on 'how' to achieve the perfect armour on both your infantry and tanks, then decide what to do. To paint that lot ups is going to also take an assembly line to do. But a little experimentation, trail and error could work wonders for you and your project. So are you looking for a way to airbrush in a few a number of coats as possible and how to wash the minis for the best effect?
Then you got 300 bases to worry about :D