No problem:
1) The original canti brakes don't have any markings but I believe they are Shimano. Mine were originally very poor so I bought some replacements hoping for an improvement only to find they didn't fit due to the mounting points being too narrow. If buying again these are the ones I'd be looking at:
https://www.sjscycles.co.uk/brakes/front-shimano-altus-ct91-cantilever-brakes-silver/ (Incidentally, after playing round with adjustment I made my existing brakes work brilliantly.
2) Not a silly question. The wheel size is indeed 700C. Original fitment was Shimano Parallax hubs laced to Mavic rims. If replacing (which I'll have to do in the not too distant future) my personal choice would be Deore hubs and Exal LX17 rims. (Should have mentioned, rear spacing is MTB 135mm not race bike 130mm)
3) I bought the bike fitted with a flat bar and inappropriate V brake levers. My rebuild was with T
ektro RL340 brake levers,
Tektro Cross Brake Levers, and
Shimano Dura Ace bar-end shifters.
4) Mine was originally 3x8 speed but the rebuild made it a 3x9 speed with 24-34-46 chainrings and an 11-34 cassette. I very much like this setup which will go plenty quick enough for me and will climb pretty much anything in my area.
5) I'm still on the original headset after a stripdown and regrease. Don't know what make it is. The handlebar I chose has a 26mm clamp area so I went for this stem in an 80mm reach:
https://www.sjscycles.co.uk/stems/100-systemex-1-inch-quill-stem-260mm-clamp-silver/ which suits me.