Okay. So ive got a couple of things to say. lol
Firstly, i think you have a good build going here. Considering the flight manipulation and stabilizations are questionable as well as the power source, i believe the rest of the build is quite feasible and i am definitely looking forward to more progress from you. Also, to hopefully help with some of the build, i suggest this.
The iron man suit in the movie has been built to fit different people; the main actor, and the stunt men, each obviously havign different proportions according to those people. But as far as the under carriage of the actual suit, i recommend you build it so that the under carriage fits you closely as possible while not restricting movement/airflow or what have you. In order to answer the question as to what you should do as far as fuel lines etc, consider this. In the pictures you posted ( i assume you got them from my post over at section sixteen ) of the underarmor, the person wearing the cage is inside the cage where the cage rests on the outside with quite a snug fit. Then the rest of the armor is placed ontop to shield the inside workings, so i believe it would be the best idea to make the actual cage as snug but comfortable as possible, and then to attach the hoses and everything else (electronics, controls, power sources, etc, ) ontop of the cage and then the plating. For example, here is a picture that i hope helps with your leg dilemma. I believe you should make the piece open at the bottom of the ankle just like in the movie. It seems to work for the actual props, and seems sensible enough for the tubing and wiring as far as space is concerned. For the extras, you can use this (picture below) note, all the pieces needed for the control of the engine is in the rear of the leg, but dont forget there are also pieces used all around the leg if you look at the picture of tony in his garage where he works on the boots. Not everything is covered in the back of the leg. hope this picture helps and i hope i didnt confuse you. Let me know if you need any other pics of the underarmor. I have the whole file. Cheers!