I have a fair amount of playtime with the Slann - here are my suggestions.
1. Guard is best on a linefrog who has doubles. I've had some luck with it on a catcher, but it's only a matter of time until someone pastes that guy. Even a blodging 7 AV guy doesn't like being in the middle of a cage.
2. See above.
3. Dodge is always my first skill. Then it's Block or Sure hands. Most often block. I don't SH all of my catchers. I also have not taken catch. They do almost everything on a 2+ and since they don't one turn score, you can spread out the risk - it's not often he has to make more than two 2+ rolls in a turn.
I don't run four blitzers. It's just too pricey and, though I like the blitzers, they are slow to develop and often get hurt before they get the chance to really progress. Playing with them is a definite must - I just don't think most teams can handle all four. Four catchers is generally great, though my team had a linefrog get +AG, so I haven't purchased the 4th catcher. I generally go wrestle on the linefrogs, block on the blitzers and catchers. I do understand that wrestle may also be popular on the blitzers, but I have gone block on all of mine - I'd rather a person hit me and stay standing next to my diving tackle. I can understand wanting to wrestle them down, though.
Blitzers on the Slann team aren't really blitzers on defense - they are more like a safety, forming a diving tackle net where you can. On defense, I really blitz almost exclusively with linefrogs since they are the ones who ball hunt the best on the team (wrestle, strip ball, tackle). I have blitzed with blitzers, but it's most often if I am hunting someone other than the ball carrier.
My team, currently 6-1:
http://iowa.bloodbowlleague.com/default.asp?p=tm&t=21j