You WILL be doing much or most of your sailing in subplaning conditions. That is how the real world. You have to have gear that makes it FUN in those conditions, that is what generates pleasure, generates Time-On-Water, generates skill growth.
The tool to do this is a Phantom 320 (if you buy from the Starboard range). It will take you from a beginner stage with a 6.5 m2 sail (or smaler for your wife) straight up to 8.5 m2 sails for effective lightwind, or blasting in high winds with your 6.5. Based on my experience with long boards (Kone One) I can tell you that speeds up to at least 28-29 knots are perfectly doable on the 320 (and that is fast!).
A P320 is perfect for your wife as well. No worries about that. And if you get a second one you can sail together, cruise all over the lake (a P320 is effective upwind as well), and hone your skills against each other.