You should absolutely start looking now. When you're armed with research about what's available in your market, reasonable prices, etc. then you can pull the trigger easily when it's time to buy. I think buyers who don't know their area are the ones that drag their feet from house to house. Definitely narrow down your locations. That way you won't be tempted by the perfect house in the wrong neighborhood.
Ditto OPs about the list. Try to target things that cannot change - e.g., location (including school district, nature of the neighborhood, quiet street), size of the lot, etc.