Oh man - I can't wait to see the tank on the stand. Sump looks great in place, too.
As for the space above the tank....I think that 14" should be fine. What kind of reflectors are you using? I would make sure there is enough room for the reflectors. How far off the water surface were you planning on having the bulbs?
With regards to the overflow - as Detri posted, I think it will depend on your return pump. You want to have your drains large enough that they provide the sump with enough water for the return pump. (i.e. you don't want your return pump sucking the sump dry because there isn't enough water brought to the sump by the drains).
Hope this helps.