Only space I know of that's needed, between hives --> space enough to fit the equipment you are using (and will use in the future), space enough to access the bees for manipulations and inspections, and space enough so each hive can access the outside world for ventilation and forage.
In principle, you can put the hives tight up to each other--but then you have trouble fitting on the roofs. So from the practical aspect, leave them far enough apart to allow the rims of the roofs to fit on.
However, to be realy practical, it's best to leave enough space between the hives to allow you to work between them, putting parts down on the ground as needed.
If you place a long row of hives against each other (working the hives from behind) it's good advice to make some sort of marking on the fronts of the hives (like a splotch of some different colors) so as to minimize wandering between hives.
I use migratory covers and place my hives close up next to each other in pairs, on a rail stand. I place the pairs far enough apart to be able to set a hive box comfortably inbetween pairs on the rails. I can use the top of one as a shelf to set smoker or spray bottle or other items on, as I'm working in it's neighbor hive. I've seen pics of hives for a long row that are all butted up right next to each other. I don't think there is a minimum distance needed between hives for the bees, it's for us beeks that need some space at times for working the hives they way we have them setup.
I like to keep mine about 3 feet apart. It slows drifting a bit, gives me something to put my stuff on when I'm working the next hive.
The one quirky thing that I like to do when working my hives is I almost always approach them from the same side.(I like the front of the hive to be on my left) I don't know why, but when I for some reason or another, have to work a hive from the opposite side, I just don't feel as comfortable. Seems backwards to me! I have never worked a hive from the back, too much leaning and twisting for me.
#1 Clover is a clever solution for the ground cover in the orchard adjacent to the apiary
#2 Love cleats, especially on honey boxes (use deeps, except for comb honey - shallow)
After first harvest promised myself all honey boxes will have cleats, kept the promise
#3 No, it's Zareba, so far so good, does the work, snaps deer, bear, neighbouring dogs, and mine.
Snapped a happily intoxicated neighbour too.
Have them in both apiaries, plan to buy third this summer.