A constant water change system at its basic level uses a pump to pull water out and replace the same amount automatically. One of the easiest is to have two ATO setups... one for the water change and the other to handle your evap. Using the controller or timers.. you shut the ATO for RO/DI off... then activate the change system. You'll pump water out, then using the float valve, pump water into the tank to replace what you pumped out. The timers will then deactivate that system and fire up the RO/DI top off like normal. This insures you remove/replace the same saltwater volume quickly and efficiently... and then shut it off and allow evap to be handled via the normal ATO system. The purpose is not only to reduce the amount of work you need to do, but will insure your parms are stable and remove nitrates etc. It takes time to tune it, but once you get it going, all you need to do is keep your saltwater mixed and check salinity once a week to insure your stable.
On a 1000G, you'll want to do about 25% weekly depending on load... so figure 35G a day roughly for 245 gallons a week. You can adjust that as needed of course.
Since you are not doing a DSB... whats the overall plan for nitrate/PO4 control? The skimmer will help considerably of course as will the constant water changes. You'll want to think about what else you will do to help with that if you find Nitrates and PO4 to be piling up once things are going. That is something you can tackle down the road, but you'll want to think about what methods youll use should it become needed. Pellets, Sulphur Reactor etc... or larger changes.
