mate, its good that you are going for a conservative dose, but 20mg is little low, you could do your first week at 20, and if all goes well, bump it up to 30. seeing you are running a liver supp, it may also be an idea to extend to 6 weeks. its bullshit when people say you will lose everything after a dbol only cycle, but 4 weeks is a little short, your body needs a little time to become "used" to the new muscle.
and at 6 weeks, you are highly likely to recover just fine, without the need for hcg. forget about nolva on cycle, keep that for pct. i would suggest getting hold of some arimidex and keep that for on cycle oestrogen control-if your nips start getting sore/puffy, or you begin holding far too much water.