Guts, regarding the grapeseed oil, I'm ambivalent about it. The last time I bought oil, it was an impulse buy at Costco. EVOO was on my list, but I went with a huge bottle of grapeseed oil when a customer shared that now that's all she uses. I don't mind the olive oil flavor at all, and the grapeseed oil seems to have not much flavor.
For roasting a head of cauliflower, since I just pour oil from the bottle, I guess I use 3-4 T whatever kind and about 1 T sesame oil (it's strong, you know). Maybe I add (glug glug) about 2 T balsamic vinegar.
The seasonings I use are my "regulars." Use your "regulars." I think dried herbs would be better than fresh since fresh would burn at so high a temperature. I'll bet a sprinkling of fresh herbs would be good combined with the grated cheese at the end though. For a different spin, try different grated hard cheeses.
Sometimes I add a few garlic cloves to the sheet pan, just because I'm roasting, and save them to use in other dishes. If adding garlic, the cloves will be done after the first 20 minutes, the outsides may get a bit brown, and the insides will be very mashable.
If anyone comes up with a really delicious end result, let us know.