Ummm.. no, you need someone to watch your tank if your gone on a 30day vacation, but the most they will have to do is top off the evaporated water with freshwater and feed lightly every few days while your away. If you don't top off your sump will go dry eventually, exposing your pumps and heater, in turn probably causing a house fire.
AC2020x - Overflow is MAX drain. Think of the overflow box as the drain in your kitchen sink and the faucet as your return pump. If you have high pressure you can put more water in your sink than your drain can handle, but if you don't turn the faucet on all the way the water just keeps draining slowly. You don't have to max out the overflow box rating, actually, you want to avoid doing that because things like algae will eventually grow in there as well and slow down the rate a little over time. 700GPH is the max I would push through a 800GPH overflow box.