Sailcloth Selection:
Always approach sailcloth weight selection from the fact that yes you want your sail to fly in light winds but you don't want it to be blown when the breeze picks up. When in doubt, go for a little bit heavier cloth (especially if your boat seats at the end of a range, or if you are planning on some serious offshore sailing).

Sailcloth Firm:
The softer the cloth (in theory) the more abuse you can put on it, but the down side is that the sail shape will suffer over time as the sailcloth will stretch more. On the other hand softer finishes tend to be less noisy than firm ones.

LP:
Most cruisers are ok with a 140 or 145% genoa, really there is no need for a 155% (max #1) as preventing heeling will add to enjoyment, but since cruising boats will use the same sail in anything from 5 knots to 25 knots there is always a need to consider how to reef it.

Features:
To improve smooth furling, look for webbing on the tack and head. Also, ask for a foam luff or similar to create surface that will take sail shape into consideration when partially furled.

Protection:
The most common one is to have a Sunbrella UV cover placed on the leech and foot. Also common these days is a Dacron UV cover that sticks onto the sail for laminates or Vectran roller furling performance cruising genoas.