Before I get into anything, think loooong and hard about taking the lizard. Green iguanas, up until maturity, are extremely flighty animals. Tail whips hurt, bites hurt, and they want absolutely nothing to do with you. But no matter how much they thrash you you need to hold them or you'll have a bitey, whippy giant angry lizard on your hands. They're also fairly expensive to get settled, grow fast on proper diets, and will need a HUGE cage. They need to be fed daily as well - think of it as a scaly dog that will probably hate your guts for the first year or two. If it's "totally tame" right now as a youngster, it's either a one in a million animal or not on a proper diet / kept warm enough.
Males get very aggressive during mating season, and females will produce eggs regardless of a male being present or not. That means you either have a huge angry boy for a few months, or a female who needs an egg box and can become eggbound.

You're right, the iguana pellets are terrible. Avoid any sort of animal proteins - they can't utilize them and it can cause liver complications. This includes bugs, mice, anything alive. For the iguana salad you want about ~45% greens, ~40-45% veggies and less than 10% fruit. I choose to supplement my iguana's weekly meals with fruit snacks in the evening instead of giving it to him along with his meal. It keeps me in his good graces

Phosphorus / calcium ratios are very important. You'll be learning a lot about the nutritional make up of greens and vegetables. I would recommend calcium supplements up until ~3 years old every day. Older lizards on proper diets shouldn't require anything extra, but it won't hurt if you don't go overboard.

Avoid Romaine, iceberg, etc lettuce. They offer very little in nutrition as they are primarily water. My staples are Collard and Mustard greens, and I mix up between escarole, endives, and dandelion greens (not the flower, just the stalks / leaves) for variety.
Veggie staples are green beans, butternut squash (any soft squash will do), parsnip and any color of bell pepper. I like to switch up with okra, asparagus, etc. Basically, variety is king with iguana diets.

Rhubarb, and acidic fruits (oranges, grapefruit, tomatoes, etc) are best avoided. Some iguanas have bad reactions to the fruits (dibble hates them) and rhubarb is poisonous. Don't go around picking dandelions or anything to feed the iguana either - unless you know for sure no chemicals were used on them, it's just not worth the risk.

For lighting you want a full spectrum UVA / UVB light. Make sure to read the boxes closely - some bulbs will say they're full spectrum, but don't include UVA. I would recommend, and use myself, fluorescent tubes. I believe ours is 10.0 ZooMed tube, but I lost the box, heh. You'll want to replace the UV every ~6 months, as it starts to become less effective after that amount of time.

I kept Dibble on outdoor carpet for a time, but it's a pain in the butt to clean. He's been on newspaper for almost three years now and has had no ill effects. (Other than smearing his poo everywhere, ugh)

65-70% is the ideal humidity. Given how large the cages are, it can be a real challenge keeping it up. Some people use humidifiers, some are able to spritz the iguana and enclosure a few times a day with a water bottle. Big bowls of water always help. Dibble gets a bath every other day to make sure he stays hydrated. Baths also help with taming down (ensures you're interacting with them) and good hygiene.

You want to use heat lamps to create a basking spot for them. You want a basking spot just under ~90F and ambience no lower than 80F. I've had to use Ceramic Heat Emitters (2) and a heat lamp to keep dibble's cage to proper temperature, but his cage is massive. UTHs are pretty useless for iguanas. Ensure there's a day / night cycle (this is why I like CHEs), or you will have a very stressed lizard. Dibble's lights are on 8am-8pm. I keep the ceramics on 24/7 to ensure the nightdrop isn't severe.

Cage size. Green iguanas are arboreal, and need a tall cage. You'll be building one or ordering a (expensive) custom built one. Six feet tall is a minimum height. You want the width to be at least half as long as the iguana (assume a 6ft long lizard). I would recommend at least 4ft long. 6'x6'x6' is even better. 10'x10'x10' is perfect. Have a whole room to give the lizard? By all means!

Tanks are terrible for them and they will outgrow even the largest aquariums very quickly, not to mention they don't have the height required for a green iguana to thrive.

Hope this helps - after you get through the hell years, and get everything set up and going they really are awesome pets! I wouldn't trade Dibble for the world.

http://www.greenigsociety.org/home.html Is very good for info, by the by.