Foresight? Maybe, but…

OP - is the road bike you are converting that Defy? I can not help but wonder at the wisdom of actually converting a really nice Ultegra equipped road bike to a single-speed as an experiment? Especially in a very hilly city?

Sounds like I may be too late to the party (as usual), but why not leave it as is and just not shift if you want to see how riding a SS bike works for you? Or pick your gear and tighten the chain so that you cannot shift if you are afraid you will be unable to resist shifting?

Good luck & have fun whatever you decide…