zandor is away on vacation but will be back soon...in the meantime;

i use flat white paint but have used mylar in the past and found the most efficeint way of using either is by keeping them (i use portable walls) as close to the edge of the growing area as possible. and spacing will help but the lower branches don't get much anyway so i think it's best to use them as clones and concentrate on the canopy.

2kw is a bit overkill for 20 plants, if ya ask me. not much, but you'll have room for another 6 or so easily. or cut off a few and use only 1 1kw. i do the same amount (20-25) but under 2 430's and bring in a 1kw for flowering.

light movers are a major addition! wish i had one now and probably will for next winter's grow. until then i'll let someone else answer that one...