Will you contribute further, or have you become tired of developing this project? (I guess I would, it's a lot of work what you did).
Could I use the SDK to make my maps? or would that be unnecesarryYou don't need the SDK to map for HL. Only if you want to develop new functionality that goes beyond the current HL code. Some mods do this, but not all, most stuff I can think of can be done in Hammer with proper use of entities.