Re:
I’d give it a service, make sure everything works ok and ride it as it is.
Don’t bother converting to drops, leave it as it is. It’ll be expensive and it’s fairly pointless. Butterfly bars are a good idea as you keep all your current contour so it won’t cost much.
Might be worth upgrading to v brakes (Halfords do a nice full set up fairly cheaply) but well set up cantis would work ok unless you are very heavily laden or in very hilly areas. Also if you go for drops the brakes will be even worse.
If it was me on that bike (which is really nice) I’d fit some newer tyres, proper mudguards and a rack, maybe some new pedals (and seat/grips if they don’t suit you) and ride as it is. If the drivetrain isn’t worn I’d leave it.
Spend the money on the trip not the bike!!