Hi Phil
If you're doing a Nile cruise, you'll probably do excursions to both Temples of Karnak and Luxor, plus the Valley of the Kings and Queens and the Temple of Hatshepsut as part of the cruise.
We went on our own to Luxor Temple at night, it's quite different to see things floodlit. We also revisited Karnak on our own as we are very interested in temples and it's so vast that you only hit the highlights on the cruise.
The Museum is very good and definitely worth a visit.
There is also a mummification museum on the promenade, but it's quite small.
If you are really interested in temples, Abydos and Dendera (a full day tour) are impressive. You can also visit Dendera on its own as a day cruise.
There are lots of places in Luxor where you can book your tours, these include things like camel rides and an evening in a fellah tent.
You will proably be offered a sunrise balloon ride as one of your optional excursions during the cruise. My husband did this in October and paid £70 to Thomas Cook. When they arrived at the balloon site, some people had paid £99 (with a different UK holiday company), some had paid £80 and one person who had booked direct at the shop (Magic Horizon Balloons) had paid £60.
You can book sailings on a felucca anywhere along the promenade, in fact you might be hard put to say 'no' as every few yards you will be approached and asked if you're interested.
We did the overnight trip to Cairo from Luxor on the 'sitting train' - it was very comfortable - but a very tiring day.
Enjoy your trip.
Polly