Ok, I gotta say I don't have any experience with fluoros, but what I can say is you should go ahead and buy 3-4 more high wattage fluoros like you're planning. Are they cool (5000 kelvin and up- white/blue light) or warm (2700 Kelvin- more reddish)? Cool fluoros are best for vegging/seedlings and warm are the best for flowering. So the best thing would be to have both the entire time or to switch them out between veg/flower cycles. I think you may be able to veg under warms or vice versa, but its only a small amount of light from the spectrum you need so you would need a whole lot more lumens. Definitely keep the fluoros as close to plants as possible without burning them (which is where the fan comes in).

If there is a hydroponic store or a big general plant nursury near you, you should try to look for some HIDs- high pressure sodium or metal halide. I think it might save money in the end rather than having to have 5 or more various fluorescents esp. if you have to change them out between cycles.

Mylar isn't a paint, its a reflective, silvery material. You can go to a hardware store, though, and look for some kind of insulation meant to reflect light. Probably ask someone there for help with that. Otherwise, if all else fails, paint everything white for maximum reflection.

As for the fan, I would recommend a computer fan or two. You could probably pick some up for cheap from a computer store assuming you have one where you live. You could put one for intake and one for exhaust or have two for exhaust and nothing but a hole for intake (passive intake). Calculate the cubic feet of your grow room. The CFM= cubic feet/minute of the fan. If the grow room is 40 cubic feet, a 40 CFM fan clears the entire volume of air in 1 minute. Try to get something that clears the room at least once a minute, probably more.

Good luck!