Hi CDG,
Tulamben is about 2.5-3hrs from 'downtown' Bali-Airport area. Staying in Tulamben for 4 nights will get you diving the Tulamben sites (liberty wreck, drop off, coral garden), Amed, and Seraya (muck) as they are only about 1hr away from Tulamben. Staying in Tulamben is a good plan...