My advice: cancel the two new accounts. Use two of your existing accounts to send RAF invites to 3 new accounts. Level 2 old and the 3 new accounts all under RAF. Transfer one of the toons at 60 to the original 1/3 accounts that get left out and cancel the empty account. With RAF, you will get the 3 new mages to level 8 in an hour.

Sorry, although this will cost you a little more cash upfront it's not actually much in the long run of keeping multiple accounts open. I can't imagine leveling toons to 60 anymore, especially boxing, without the 3X bonus.

Once you've tried it you will never go back.

As far as mixing up the group, adding a healer, that depends on what you want to do later on. Pure teams are a little easier upfront because the macros are all the same, and they level absolutely fine. I brought up a group of 5 mages and maybe I died once or twice (PvP server), never to PvE. I think 5 mages are great for leveling.