So in the end it really depends on the mold maker for how detailed (if any) 2D drawings should be. In the past my drawings have only shown design specific features for the mold (rib thickness, various fillets at the inner corners, draft, threads if they are present, etc.) and locations of any locking or hole features. As @drawoh mentioned, GD&T is the best way to establish the locations of locking and hole features. Fortunately due to the nature of plastics and mating components the tolerances are fairly loose and can be easy/cheap to inspect.
On the other hand, I've heard of mold makers requiring fully defined 2D drawings. This can be tough if the plastics have a lot of non critical features (aesthetics, locations of ribs, etc.). You should be able to find plenty of mold makers that don't require this though.
On the other other hand, some mold makers don't need 2D drawings at all. This can work if the design is simple enough and locations of features is not paramount. If you can 3D print the design on an FDM and it works then you *probably* don't need drawings.
My suggestion would be to detail the drawings to what you feel is necessary and send it out as a quote/evaluation package, even mentioning it is your first time. I've done this in the past when working on new manufacturing/processing projects and ended up working with decent shops willing to point some things out to me.