Your questions make me wonder whether you've been to look at a few narrowboats before asking because, if you haven't, I think you could have asked better targeted ones in this sector if you had.
There are many different boats, with different layouts, different lifestyles and usage patterns and different equipment fits according to budget and other factors. Anyway, here's my input for what it's worth :
1. Nothing that I wouldn't have difficulty cooking elsewhere given an oven, grill and 4 burner gas hob. That said, the dedicated marine freestanding oven is a bit smaller and less accurate in terms of control and temperature than a decent household one, so it takes some adjustment.
2. As above, but the oven characteristics are slightly more of an issue.
3. In a cupboard or the fridge, probably mostly fresh ingredients.
4. Flambe? Being a confined space, the limitations are ones of safety and common sense.
5. That's a strange question. There are already floating cafés and canals are often narrow, so a floating allotment is likely to be a hazard to navigation. I'd like to be able to have better, more reliable access to moorings at supermarkets and the like which are frequently poor or full.
I hope that helps get you started