I don't really know why slopes are better - I assume just because each vine gets more sunshine, not sure it has much to do with drainage. We used to live in Switzerland where there are a lot of vineyards and I got the impression that the poor, sloping land could be used for vineyards whereas livestock and arable crops made better use of the flat ground. They don't mind cold winters, they're dormant through that and many of the traditional grape growing regions have harsh winters, but they do need a lot of warm sun in summer and I think that will be more of your struggle. We battle mildew here when the weather is too damp and I imagine our climate is a lot drier than yours!
Our vines are all managed the same. We're using the Scott Henry trellis system which maximises yield from a small area (apparently). It's not used commercially because it's too much faff and still not really sure it'll work for us because my husband, whose baby this really is, is struggling to find the time to train them. They were planted in 2014, then first winter after that we pruned them all back to just a couple of buds so about 8 inches high, then last year they grew more massively and so for winter pruning, many were taken back to about 1m high which is the trunk to be. Spring time all the buds but the top two or three are removed and these form the shoots that will run along the trellis. With Scott Henry you end up with a double system where you pull the bottom level of shoots down and the top lot are trained along a higher wire to give them all space and exposure to the sun. It is all pretty time consuming and we also use vast amounts of chemicals (which was not the original intention) to kill the weeds, feed them, prevent mildew etc. etc. But if you have fewer, you might be able to do more by hand. We also receive a regular bulletin sharing the weather forecast and prompting us what would be should be doing.
I can't see that an English red could ever really live up to international competition - even under cover I'd have thought it would struggle. But with pinot noir we hope to be able to produce sparkling whites, still whites, sparkling rose and still rose. Certainly Chapel Down is not very far from us and their wines are gorgeous - cheapest bottle of still white retails at just under £10 with sparkling whites and roses going up over £30. Just not sure whether these prices are attainable for our sort of scale particularly as it's such a growing supply here with more and more vineyards being established.