I often use Deflect (All Attacks +3 and Free Action +2) as an alternate power of Super Speed to represent how hard it is for them to be hit.
1. Do you ink this is a fair way to represent how hard it is to land a hit on Fast Characters?
2. Is the attack only rolled once for the Defense & Deflect or do they have to roll once for deflect and again for defense?
Re: Deflection Question
You can't do this in 3e, and you probably described why they changed that from 2e.
If you want a speedster who can't be hit, take a look at Power Profiles. They have suggested powers such as Immunity to Dodge/Parry, Concentration duration (so somewhat cheaper). You can make yourself impossible to hit, but you're effectively using total defense.
Or... Alternate Effect: Insubstantial 4 (perhaps with a lot of Affects Corporeal, so you can actually do stuff). Or just outright Immunity to Dodge and Parry, perhaps with a Quirk that it doesn't work if you're unaware of the attack. Those are probably what you want, but that's expensive, as it should be.