You are on the right track.. 4 ft is really tough to grow in, but autos will fit in there.
You will want 2 autos in 3 gallon pots and around 150 true watts of light for each plant. Northern Lights x Big Bud Feminized Auto is full proof. I don't think anyone could mess it up and it's just an all around great plant to start with.
Forget hempy. That's an advanced technique. You will F up the PH or burn nute burn them or have cal mag deficiency.Go with quality soil such as Fox Farms or something comparable. DO NOT use any SCOTTS or MIRACLE GROW PRODUCTS.
For lights you need something that doesn't require a lot of height. You'll have to rig a bunch of CFL's. I hear that certain 99c stores have the 150w (42 true watts) equivalent bulbs for 99c. I'd say try t5, but you would need 3ft t5's and they're not so common.
A MARS hydro LED would probably be good in that space also.
Two 150w Sun Systems HPS lamps would also be great.
Your biggest thing to consider will be ventilation and stink control. There is no way around it. You have to purchase an inline fan and carbon filter. I saw 4 inch hurricane fans 180 cfm and 200 cfm Phresh Filters combos for around $120. That's about as inexpensive as you can go. It's still a very effective rig.