Bear in mind that the easy standouts are the most-desired ones. Your plan is to save money over the cost of a new bike, right?
The nice thing about older bikes is that they often have more tire and fender clearance, so you may be able to combine several of your planned builds into a couple very flexible builds. Heck, google "650B conversion" and you may be able to make one bike do all of those jobs.
Check out the English 3-speed thread for some bikes that will do the city and bad-weather riding for a low price.