So following this post, it depends on what you want.
Additionaly to above link, which mainly consits of the theoretical part and I highly recommend you to read as you still seem to make up those kinds of decisions, I'd like to give you an advice on how I handle this.
The best thing to do, in my honest opinion, is to wait. Either you wait until you have got 125 candies and evolve then the best out of the contesting Squirtles, or if you're lucky enough to find say a Wartortle you can evolve it too instead of a Squirtle.
The main aspect in this approach is that evolving as soon as you have 25 candies is mainly pointless (unless you just want the Wartortle or highly depend on it as your main pokemon [for winning fights etc.]). Say you evolve at 25 candies, you get a decent Wartortle and just as you're about to farm for more candies you find a better Wartortle.
i) It depends on your playstyle. Do what you're most confortable with.
ii) I'd suggest to wait until you can fully evolve your Squirtle into Blastoise.