If you know someone with built wheels, you can test out the fits with wider tires and measure the brake reach needed. Also if fenders are feasible.

As Bulgie stated and you observed, this is likely french threaded. If you look at the BB cups, sometimes they are noted (35X1 French, 36x24 Italian (almost certainly not), or BSA (1.37 X 24)). Confirm before coimmiting to anything. Remember, cranks match up with the BB spindle length, so measure the length of the spindle and you can narrow down the crank it had.
--Since it is a Sugino bottom bracket, it likely is Campy and early Japanese compatible (ISO taper), and will likely not play well with modern Shimano cranks.

A Brooks saddle draws attention. You can likely grab something less interesting (I am a big fan of Terry Liberator/Dragonfly models and they don't show off). Alternately, you can get a quick release binder bolt and take it with you! Haha. Or one of the waterproof Brooks saddles with the cutout. C15, C17, C19 I think.

As far as components specifically...
1. Drop or straight bars?
2. Do you want indexed shifting? Down tube, bars (straight bar), bar ends or brifters?
3. Racks or not?
4. Triple crank and/or wide range gearing in the back?