Claude Butler 'to do all'

I often keep half an eye out for a CB for similar reasons.

. Fit 30c tyres

Are they definitely 700c? Wondering if an old CB would be 27". I which case you might be in luck clearance wise.

. Add water bottles cages. Bike currently has 2 holes, any creative ways to be able to hold 2 bottles?

First I'd work out why you want two bottles. If you need more water you can always keep it stored somewhere else then swap the bottles over. But you can get things called rivnuts which would allow you to add extra bottle bosses.

. Find some way of being able to hold food + tools for the bike - something for the main triangle?

Not very on trend, but for what you've described there I'd get a bar bag and a small saddle bag.