Don't buy the gear now, first take the lessons, that way you and your wife will learn what type of depower system you like more. I personally prefer over the bar depower, as I think its safer and doesn't damages the rope like other systems do.
After the lessons, go to the place you will be practicing the sport, talk to local kitesurfers and learn how strong is the wind in that place, how flat is the water and the seasons to practice. Then you will have more insight on the size of the kite needed, as it depends mostly on the strength of the wind and your weight.
When you are ready to buy, I recommend you get a good used equipment, because as beginners we tend to wear the equipment faster as we learn how not to "windenburg" the kite (crash it). This equipment should be good to use for about one or two years, after that you will have enough knowledge and experience to buy the perfect kite for you guys.
I just finished a couple articles: Kitesurfing for Beginners
and Kitesurfing Gear
explaining how to ride and what equipment is needed. I would really appreciate your feedback on them as really nobody has read them yet and I really think they are useful for you