That's my gear arrangement:
http://home.comcast.net/~jeff_wills/...-grr%20006.htm
http://home.comcast.net/~jeff_wills/...-grr%20008.htm

The 24/34 allows me to climb 15% hills with a touring load. It's barely faster than walking, but if I wanted to walk I wouldn't be on my bike.

The answer to the chain length question is that the chain should be long enough to go around the big chainring/big cog combination and through the derailleur. You probably won't be using the small chainring with the smallest 4 or 5 cogs- shift up to the middle chainring and big cog when the hill allows it.

You should never make the chain "too short". You might think you won't ever shift into the big chainring/big cog combination, but some day you'll be at the end of a long day, tired & dopey & forgetful. That's when you'll shift into the big/big... if the chain is too short, you'll be lucky if it just jams. You can bend or break things by forcing this shift.