55 gallon: Too narrow front to back. If you can handle the 4' long, then look for the widest (front to back) tank you can fit in that space. The wider the tank the better the layout.
Filter: If you want a Hang On Back style, go with the Aquaclear product line. These have the best arrangement of media.
Yes, the more front to back depth the better if you space will allow.
I like the Aquaclear for the large Media box. I also like that the AC 20 to AC 70 Impeller are interchangeable to offer additional flow speed options (per an email from AquaClear)
The simpler you can run design the system the more time you'll have to enjoy your tank.