I don't have any experience with a fuges so I'll leave that to someone else. I will tell you though that if you are going to use a sump that in general, bigger is better. The sump adds to the total water volume of your system. That extra volume of water will help if something happens with your water chemistry.
A 45 gallon tank with a 30 gallon sump is just like having a 75 gallon tank as far as water volume is concerned. Obviously not as much room in the main tank though.
Just remember that whatever equipment you add to the sump will displace water and alter the amount it will hold. Since my sump has a skimmer in it along with the heater and return pump, it doesn't really hold 10 gallons. You will also need to leave room in your sump to accomodate the water coming down from your main tank should you have a power failure to your return pump. You don't want the sump to overflow!
IMO, a sump is definitely worthwhile if you have the room. There is nothing showing in my main tank other than the overflow box, the return pipe from the sump and a couple of powerheads for water current. To me that looks much better than a bunch of stuff hanging all over the back wall of the tank and the more water volume the better.