I am no expert, all I can do is give you my experience.
Last year in Serbia was extremely hot and dry. Since grapes like it that way, my grapes although totally unattended, grew and yielded beautifully. I only needed to irrigate it occasionally.
In response to black rot, there are two ways my late father used: one is to raise your grapes higher than 1.5 meters to prevent evaporation from the soil to reach leafs. Spreading some rocks around the base of the grape is helpful also. Sepp Holzer talks about it too. Rocks, and concrete blocks ( or pieces of broken concrete) serve as suntraps, containing the heat and helping maintain favorable microclimate.
As for support plants, ordinary grass and for that matter any plants under the grapes that help prevent mildew and high humidity are helpful.
Once again, these are my observations. Hope it helps.
