Tramps for a 7 year old is fine, just be careful on windier days as they can act as another sail, especially flying up off a wave, and have been known to flip AI's.
A GPS is a great idea, both for safety and quickly learning what your doing on the water. It's often hard to tell how far you are from places/objects or what direction to sail for the most direct route to a point. Also, accurate bragging rights for speed, distance and track.
Bilge Pump a must if going very far from shore, or from a safe takeout.
I use a 3 foot long 1 1/2 - 2 inch wide color ribbon tied to the top batten for my wind indicator, and to differentiate each boat.
Hobie did design the TI with a jib in mind, but it had problems in testing and is not perfected. Hull cracking between the front aka x-bars and the bow, I think.
Here's a link to a page on my website with many of my AI mods: http://www.kayakingbob.com/hobie-ai
and a page with some older forum posts of mods: http://www.kayakingbob.com/forums
- - - - - - - - - - - - - - - - - - - - - - - - - - - 2007, 2009 & 2010 Hobie AIs and a 2010 TI