I said it backward, sorry. A digital ballast will be HPS, and you can run MH with it also, but you'll need a MH conversion bulb.

If you go with 1000w, I would think a 6" fan and duct run would do best, but you may be able to get by with a 4" high output. I'm thinking 4" would be fine for a 600W. You also will need a small oscillating fan to make the plants gently rustle in the wind. This makes them strong so they can hold the weight of all those heavy buds to be. You also need some way to exchange air in the grow space, unless you are doing that at the same time with the enclosed hood. Some people run the warm air of the grow space through their cool tube or enclosed hood. I tried to make this work, but had horrible results.

Also you will have much better air flow if you use actuall ducting material and not the coiled dryer duct. Changing over totally solved the heat issue in my veg section.