Exactly - think about Budweiser - there's nowhere to hide any flaw. Stouts, porters and IPA are all good at hiding fermentation errors, because they have strong flavors. This is why many consider pilsner to be one of the tougher styles to do really well.
Totally depends on the size of the beer. Your limited by what you can mash, not boil. So you can make a much larger batch of 3% mild than 12% barley wine.
I can do 10 gallons easily in 15 gal keggles.
I put the hops in a bag and just drop it in the keg. At serving temp, it's gonna be drank before any negative occurs.
I also think the grassy thing happens with noble / low AA hops far more than with C type hops. I've never had an issue with a long dry hop of big AA american hops.
Belle saison dry is very easy to use. I would use your usual closet and not try to control the temp - just let it go. It'll probably finish within a week. I've done several beers with belle and it will end up pretty dry.
You can do it - but not with bottle conditioning.
If you try it I would overpitch a ton of yeast - ideally a big ass starter at full krausen. Give it from day 2-5 to ferment and package on day 5, leaving days 6-14 to bottle condition.
I would brew the beer and tell your buddy his birthday...
Typically you should take readings over a couple of days to be sure - but 1003 is pretty low. You should be fine. I'd test one at day 5.
Saison yeast is pretty aggressive and can certainly finish quickly.
If this is a hoppy style, you may want to dry hop (just add pellets to primary fermenter) to boost your ibu some. The lower temp would result in less hop isomerization and lower bitterness.