Yes, you usually need to be consistent with the invite/accept order of your team, and keep the same order each time. There is an advanced configuration that you can do that gets around this, but at some point you will usually come across an expectation of ordering, with Group Leaders and members. Firescue17 goes through some of the concepts here
http://isboxer.com/forum/viewtopic.php?f=6&t=4241, but some of this has moved on. Note it is a concept only and not a fully functioning setup (i.e. it requires a lot of reading and for you to do the implementation).
Yes there is a better way for rotations and healing.
DPS rotations are easily taken care of via using mapped keys to send different keystrokes to different toons. This is taken further by the Pro Config
http://www.isboxer.com/wiki/Style:MMO_-_Pro, which allows you to configure per class, or other defining characteristics. Also the template concept from Firescue17 I linked to above takes this further (he has some videos linked too). Another link for the rotation concept is
http://isboxer.com/forum/viewtopic.php? ... mer#p28442. In the end, I have a single key for DPS rotations and I press it a lot. I do sometimes use another for interrupts, but it depends on what game your playing as to how many keys you end up needing.
Healing rotations can be built into the Pro Config too, although, IMO, that works best for AOE heals. For targeted heals then you might want to look at Clickbars
http://isboxer.com/forum/viewtopic.php?f=27&t=6593 (you can do the same with Menu's but it requires some custom templates), or you can use mapped keys, although the targeting I find is usually the biggest pain with that, but if you're good at remembering what keys do what, then it may be very easy to have a rotation that you can swap targets around on.