OM-D and legacy OM2 lenses how useful?

I have pre ordered a OM-D E5 as first serious camera for 20 years so I am quite inexperienced in digital field (apart from compacts) . From that time I still have an OM2 with following 4 lenses: Olympus f1.8 50mm; Olympus f2.8 35mm; Olympus f3.5-4.5 35-70mm zoom and Cimko f3.8 70-210mm zoom. I know that effectively I will have x2 factor. Queries:

1. Are these lenses ging to be useful or would I just be better replacing with new m43 lenses or a zoom?

2. I know I can buy an adaptor, looking at 3rd party adaptor as not sure if Olympus one will deal with old OM2 and is expensive. Any suggestions? The Kiwifotos has come up but sure there must be others ( I am UK based).

3. How do you use the lenses practically? I know it will be effectively manual and autofocus does not work etc. You will be able to set the aperture on the lens manually but what do you then set the camera, auto, aperture priority etc.. to manage exposure correctly.

Any advice would be most welcome.

thanks

Paul