It is allowed. I think the only rule that specifically apply to multiboxing is that you are not allowed to use more than 5 characters at the same time outside of raid instances.
I think the best way to level a multiboxing team is inside dungeons (until level 58, questing after that) because you don't have to travel and you can't get ganked.
If you have a good setup you can aoe the enemies down very fast with no drinking downtime. (I don't like your setup, it is good if you want to have many different classes but it will be slow at clearing dungeons and it will likely struggle against 3+ players in pvp)
Like Xandor mentioned, it's a perfectly valid way of multiboxing and within the rules. Also very correct when it comes to leveling and how to approach it. I'd however add that if possible, just boost those characters with a main and use gold for gear if possible. If that's however not a possibility, go slow and steady and sell everything along the journey to the AH.
Not certain regarding his comment about the setup however, imho it's just fine. Perhaps not the best for PvP (wouldn't comment on that, as that's not my thing) but for pve it'll do just fine. Rule of thumb is, direct damage is better on shorter fights, so when clearing trash priests can be little gimmicky. They however can be great healers and via smart use of different rotations great all arounders as shadow too.
Just remember if you ever wish to box above the limit of five characters, it has to happen inside a raid.
I've ran spesifically these classes in heroics back when I did 5man boxing with zero issues. Still include these classes in my 10man raids as well as 25.
Thanks for the clarification, xandor and Raidenes.
I'll go ahead with the characters that I already have, but also take onboard xandor's advice and I'll also get a team of identical druids/shamans/etc eventually. I'm also new to multiboxing and taking up the learning curve of HotKeyNet while I'm at it. I'm just glad that 5-man dungeoning is allowed, I'm definitely not botting anything and just keycloning to the 5 windows.
is it allowed in 5v5? I'd like to test how far I can push a multibox team
It is allowed but almost no one plays 5v5. I have tried and I think it is fun to play 5v5 (I have won against 5 regular players with an average of ~500 higher gear score than me and I think another at least 10 different teams with similar or better gear than me, but once they start exploiting my weakness I have no chance of winning). Was fun to fight the different multiboxing teams in there also.
The issue is that basically no one queue. Several times I stayed in queue for 14+ hours with no arena popping.
Another issue is that wintraders queue 5v5 sometimes and you can get banned from getting free wins from wintraders even if you try to avoid them but they are persistent and queue into you at random times.
I stopped queuing when they played but then after maybe 4-12 hours later they started queuing again and I got another win, that happened a few times and I got banned for half a year because of it even though I tried my best to avoid them and reported them.
It is also against the rules to arrange fights. You can't ask other multiboxers or anyone else to queue against you in 5v5. It has to happen randomly.