I want to start a map for dod source and was wondering which way would be best... Should I start in CSS and port it over or should I do it on the HL engine and port it over? If I do CSS what does converting it to dod going to entail? willl I lose all texture information or do they overlap? what will converting entities be like?

Make a basic layout map for DoD v1.3 just to test the gameplay, then port it for HL2DM or CS: Source to start playing with the entities, effects, etc, then when DoD: Source comes out, convert the Source version to DoD: Source.