Oh you do need a stove. You saw how productive that man on Slubber's thread was with his home office and everything. It's just not doable whilst freezing your arse off. 
Other questions:
No need to waterproof. Apparently canvas swells out once wet for the first time and that waterproofs it, but we had rain first time we used it and not a drop came through.
Do I need anti mildew stuff?
Nope, no anti mildew. Essential to put it away bone dry though (see ref to stove ). We're come home with it borderline and just draped it over the doors for a day or two.
Fireproof. I've got mixed feelings on this. If you don't have a stove or plan to ever use candles, I wouldn't bother. Opinions vary, but I've read a couple of articles saying that fire retardant treatment gives you an extra minute or so once on fire, but that's about it. A knife under your pillow, wool blanket and carbon monoxide and fire alarms much more useful imo. If not planning on fire, a fire bucket at front should be enough. (btw, even "fire retardant" synthetic tents will burn pretty quickly, so I don't think canvas more dangerous really). There is a You Tube video somewhere where they demonstrates to children on a camp.Treatment also means it won't last as long. Can't remember why probably making this up.
We always store separately at camp, as groundsheet more often than not damp from the ground. Just bang groundsheet in bin bag, and once home check it's 100% dry then put in canvas bag on top of other tent.
Not sure about the cupcakes - dh lives in hope. However, axes and storm kettles have a way of sneaking in...
We usually pitch under trees, but only because that's the kind of sites we usually got to (in woodlands etc). Leaves do fall on the canvas - doesn't stain it, but if a completely clean tent is essential to you, it might be worth waiting a bit to see how you feel.
We've never had a leak, even through one really, really stormy night.
We store ours either under the stairs in the hallway or in our bedroom. I'm too nervous to risk it getting mouldy in shed or mouse-breakfast.