#2: Depending on your water table, leaving a pool empty is very risky. I would not leave it empty any longer than you absolutely have to. The weight of the water helps keep it in the ground and not floating.
#4: It would be significantly warmer with darker color. Check out pooldoc's recent post here: http://www.poolforum.com/pf2/showthr...856#post104856 Although he was talking about paint, the effect should be the same with a colored liner.
#6: If the niche is under concrete, you probably aren't going to be changing it without busting the concrete up. You should be able to replace the light and use the existing niche without a problem, though.
#7: My understanding is that you never really need to change the sand media. You can if you want, but bleach and a backwash with clean water should do the needful too. If you decide you want to change it, do it whenever suits you best.
When you're filling the newly lined pool, get chlorine in it asap so you don't fall behind. Be sure to use really small doses and test often while filling so you don't bleach out the new liner if you choose something other than white.
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