These questions are always hard because every one's different in how they think/react, class combo, and number of toons. For example, your setup is more complex than my 5 box because I only run 2 classes (Pally + 4shaman), so I'm basically 2 boxing.

Pretty much I'd say if it feels intuitive for you then it's probably fine. As you progress and encounter more complex scenarios then you'll naturally morph what you do a bit. I wouldn't worry too much until you hit a wall on something, then start reconsidering. Once the abilities start stacking up then it starts getting a little overwhelming and I think everybody has to reconsider how they do things but trying to plan for that at this level without a LOT of prior experience is tough.

I found personally that I was a lot happier once I replaced my nuke action bar buttons with cast macro's like this
/cast [target=party1target] Lightning Bolt
(note this doesn't work if you're main isn't leader so you may need to replace party1target with the name of your main)
World mobs die so fast I was just wearing myself out with [assist][nuke][nuke][follow][assist][nuke][nuke][follow]
At this point it doesn't seem like a lot extra but it wears over time and the more abilities you get the more you're going to want to simplify what you can.

Also, it sounds like you're pseudo tanking with your shaman and I don't really think that's the way to go. I tried it, quite literally up through 34 and was not happy with the results. Shield and Leather (at that level) just still can't take much of a beating and you've got nothing other than your dmg threat to keep their attention. It seems like the high end 5x shaman crew go straight for the crazy DPS strat and I think it'd serve you well too. In my case I had a 34 pally I could replace my 5th shaman with so I went ahead and "wuss'd" out. So, depending on what you want to do in the instances you may reconsider. Either have all 3 go crazy DPS or swap in a tank for your shammy.

If you want to be the healer of a 5man with 2 DPS, then I'd move the priest healing stuff off to a 2nd keyboard (nostromo, etc.). I dual boxed with tank/priest this way for over a year and was very successful with it.

I will say though that 3 DPS LFG could take you a while to find a tank and healer, and if they're not friends they'll hearth out if anything goes wrong and blame you for it (regardless of weither it's your fault).

That's my $0.02 - gee, really didn't think I had anything to say on this... .too much coffee...