You can definitely get by with auto feeders. There aren't too many fish that will only eat frozen. Most fish in the industry can get by with pellet and freeze dried. You algae loving tangs will appreciate sheets of nori, but the extent will be tank size dependant. If the tank is big enough, they're likely able to forage around for quite some time. And you can provide nori intermittently. As you are researching fish, just avoid those that are finicky eaters.
The duration of how long a tank can be left alone involves too many variables to predict. The biggest issue is top off water, feeding, and monitoring the overflow (assuming you have one). Then there's dosing or CaRx maintenance if that applies to you. However, all of those things can be set up in such a way that you could technically leave it indefinitely. The problems arise when...well....the problems arise.
Something goes crazy with the overflow? That could mean trouble. Reactor has a problem? There's another ordeal. All in all, you will be the best person to determine how well your tank can cruise. You just have to recognize how often you do little adjustments or changes and then consider what it would be like if you weren't around to do them. No one should be tied down by their tank.