I think that North coast is a better location for land based diving vacation.
Even though Nusa Dua area is more developed with lots of good quality resorts there are also several good alternatives on the north.
Mostly like boutique upscale SPA resorts with more personnel service. Surrounding areas are not so developed as Nusa Dua.
However all good macro dive sites like Secret Bay or PJ are 30-40 minutes drive from the resort.
Tulamben area is still couple of hours drive so it made sense for me to spend one night at Seraya Resort and dive for two days there.
I read that you have already organized the hotel but decided to write the info above since the key for a successful land based diving vacation in Bali is the location. (unless you dont want to spend lots of time on the way)
During my stay in 2006 my dives were organized by www.diving4images.com
I had a jeep, driver and a very good and experienced dive guide, all organized by Dwi and Graham of diving4images.
Everything regarding organization of diving was in a high and very personnel level.
I would highly recommend you to contact them.
Hope this helps.