As little as possible . . .
My best advice is to avoid trying to do too much. Yes, there is a lot to do and see, but if you try to do it all, you'll miss out on the benefit of just relaxing.
With that said, my thoughts for activities are as follows:
I would recommend a whale watching trip, as February is Humpback season in the sound off of Lahaina--If you've got a good ocean view from your condo, you can probably see them from there too (bring binoculars) but it is definitely cool to see them right next you--haven't done the kayak tour, but being that close in a kayak would be cool, but actually pretty frightening (to me at least).
Road to Hana is nice, but is long even for a whole day trip. If you can spring for at least one night in Hana, or thereabouts, I would recommend it, but as a day trip, it is a very long day.
I haven't been there myself, but my wife enjoyed hiking in the Haleakala crater, but again, another longish drive. Io valley is definitely a good short trip--not really hiking, but very pretty and very interesting history too.
We've stayed up in Kapalua, which has three varied beaches (one good for snorkling, one for surfing, one for boogie boarding) within walking distance, but it's a hike from Kihei and maybe not worth it. We did go to a nice beach at kind of the end of the main road past Wailea which wouldn't be too far from you, but there are lots of nice beaches most everywhere.