Hi WB
Sounds like a nice project, nice and big too!
Re the questions
1) Substrate really depends on your budget, complete substrates like Eco-complete or ADA AS will cost a fair bit but give excellent results, base layer ones like the tetra one and tropica one are cheaper but may not give such good results. If you want a carpet of something like glosso or HC then I would get a complete substrate if you can afford it, this saves the plants having to use lots of energy sending out roots to 'find' the nutrients. If however you want a stem plant scape then a base layer would be fine.
2) I take it that if you're going to use EI then you want a high-light tank? If so then aim for around 150 to 200w over the tank. 4x 42in. lamps at 38w each would probably do the trick, or if you could get them 3x T5 46in lamps at 54w would be good, as the extra power would help the light reach the bottom of the tank. But not so sure about the length of these being 46", but worth a look all the same.
3) With all high light tanks aim for 30ppm CO2, there isn't a graduated scale like I think you are thinking. Its all or nothing really, i.e if you have high light you NEED CO2, however if you have lower light then CO2 becomes less necessary (although probably still beneficial). So get a stable 30ppm and you'll be fine.
4) Dont bother with a substrate cable, their effectiveness is questionable at best and useless at worst, spend the money on things that will definitely help, like the light or substrate.
5) Other things to consider are how much money you have to spend, how much effort you want to put into the tank, what kind of scape you wamt, and very importantly, if you do go down the high light route, get lots and I mean lots of plants into the tank when you set it up or you'll be plagued by algae.
Hope that helps
Sam