The answer is going to vary a little for everyone. Personally though:
1) I'll pick the higher IV one over the CP if it's meta-relevant or a personal favourite. High CP I'll do for for less relevant ones, but there's still usually a limit - I would still look for something that has reasonable IVs, say 85%+
2) If you're not going to use them, there's no point evolving them beyond that initial dex entry. Exception to this is for XP grinding. Save your candy just in case a future update/event makes them relevant.
3) Yes and no. While I wouldn't keep hold of every single Pidgey, I often keep hold of meta-relevant mons to trade to other players. I earn myself a tiny bit of candy and potentially give them a new lease of life with someone else.
