I've kept an archer fish (named Fluffy) in a 4' ~50 gallon/185 litre freshwater tank for about 9 months now. He's grown a fair bit, currently around 5"/12cm long and a good 1"/25mm thick in the body, will eat multiple large crickets at meal time whereas a few months ago he'd only eat one, will happily eat half a dozen 3mm pellets at a time, he's not interested in small pellets or flake food anymore.
Tank is freshwater with a few low rocks, driftwood, and lots of plants; valisneria, water sprite, hygrophyla, cryptocoryne. Maintained at 28 degrees Celsius, ph 7.5, nitrate below 15ppm. There's a lot of coral sand/shell bits in the gravel which raises the ph and I presume hardness, though I don't test for hardness.
Fluffy's been kept with dwarf gouramis, Bolivian rams, blue rams, kribensis, empire gudgeons, gold panchax (large adults), bristlenose and other small-ish fish without incident, including two spawns of kribensis. The second spawn were left to grow in the tank and reached about an inch/25mm before I removed them. Once they reached a bigger size he noticed them and would often venture down lower in the tank looking for them and chase them if he saw them, but he never seemed to try that hard and they were always quick to dart into plant cover so he never got one. He'll happily hunt and eat inch long guppies though.
He's currently sharing his tank with a thorichthis meeki, aequidens pulcher, laetacara curviceps, 3" cichlasoma octofasciatum which I'm holding for someone temporarily, an empire gudgeon, and lots of bristlenose. Until recently there was a 3" salvini in with him that he got along well with but I removed her because she was bullying the other cichlids.
The whole time I've owned him he's been one of my most healthy active and interactive fish. He's first in line for food, he'll jump from the water to grab moths or crickets from my fingers, he'll sometimes spit at insects if I hold them out of his reach, and he'll chase and spit at insects that fly into the hood or that he can see through the glass outside the tank. One time after I hadn't fed him insects for a week or two he ignored the pellets I dropped in for him and shot me right between the eyes. I got him a box of crickets that afternoon.
He's never been territorial, mostly minds his own business and is mostly happy to swim away from a fish that's defending it's part of the tank. He used to get chased by a red dwarf gourami which he wore, but I think as he got bigger he may have realised how ridiculous that was and started chasing the gourami back into his patch of foliage.
The only time he gets unhappy is when I take the hood off or do a water change. Even if the water level is only 2 or 3 inches below normal he swims up and down and back and forth against the glass frantically. Maybe he thinks he's trapped in an evaporating pond.
I've often heard people recommend only filling your archer fish tank half way and even heard a few say that it's a necessity, but I don't see it being worthwhile unless you have a particularly big tank and really want to see them shoot insects off twigs.