For the Kanchanaburi trip I would recommend River Kwai Hotel as the best place for you. It's a nice hotel located just in walking distance from most venues in the city like e.g. the Bridge on the River Kwai (2.5 km, though), the War Cemetary, and the street with most restaurant or bars . There are other hotels or resorts, but for me they are located a little bit outside the city which I think is a bit inconvenient since you will be needing some kind of transportation to and from the city.

From Kanchanaburi you can go visit the Tiger Temple, you can make an elephant trek and visit other places like the seven steps of the beautiful Erawan Waterfalls and take a train trip on the 'Death Railway'. For the tours I recommend you to contact one of the local tour agencies like 'Good Times Travel' who has daily trips for these locations.

More info about Kanchanaburi (hotels, guesthouses, restaurants, and much more):
Kanchanaburi-info.com: destination guide to Kanchanaburi Province, Thailand

Info about River Kwai Hotel:
kanchanaburi-info.com - Kanchanaburi hotels and resorts - River Kwai Hotel - Pictures and Facilities

Tour agency:
GOOD TIMES travel service - your local tour operator for tours within Kanchanaburi province (Thailand)