Seaangel,
Lahaina Divers is located in downtown Lahaina, not too far from where you will be staying--they are fine for what you propose. Maui Dive Shop runs a similar operation and they will be fine, too. Most operations will launch from the Kihei docks, a 20-30 min drive from your condo. Occasionally they launch from a closer site due to winds.
The easiest "signature" diving on Maui is the inside of Molokini. You will see a lot of dive boats for both scuba and snorkling there--but it is decent diving for a novice. You will see lots of fish. LOTS OF FISH!
The back wall can be a little more challenging if there is a strong current, but it has more spectacular diving. Normally the back wall is a drift dive and a lot of fun. The dive masters will ask about your experience level and will suggest the back wall to novices only if the current is mild. If it is your first drift dive, you will be lucky! It is wonderful!
Usually, those two dive shops will make a stop at Molokini and then go to another site for the second dive. But they normally ask divers where they would like to go--and they have been known to do the inner and outer walls of Molokini on a single trip.
Lahaina is a very busy and bustling town! If you want to go to more quiet and intimate place for dinner, try the Sea House up near Kahana--it is a 25 min drive from Puamana, but worth it. Be sure to call for reservations, though--EARLY! And ask for a seat close to the "windows" (They have no glass in them!)to get one of the best views on Maui.
Now, I am not one of the world's great shoppers, so I am probably not very helpful in that regard: but, believe me, you will have no trouble finding shops in Lahaina! When it comes to history, that is a different story!
The old missionary section of Lahaina is worth a visit--south end of town. But the "whaling ship" berthed there is not... The whaling museum at Kaanapali IS worth a visit, too. Kaanapali is few minutes north of you by car--and the museum is in the middle of another great shopping area!
If the weather is good, Haleakala is also worth the trip--whether you bike down the mountain or not. The views on a day when there are not clouds and fog are fantastic!
If you get a chance to read James Michener's HAWAII before you go, do so. It is a painless way to absorb Hawaiin history--remember, though, it is a novel and, so, not completely accurate. BUT you will learn all about Lahaina. It was once a the biggest whaling port in the Pacific. And there is lots of adventure, romance and (blush) sex in it.
Joewr