I agree with the above poster, the first thing you need to do is call a good reptile vet (if your dad has boa's he should know of one) and schedual the soonest appointment you can. A vetrinarian will be able to establish any medical problems your new ig may have, and seeming how he came from a neglectful owner its quite likely he does have some. Bring a fresh stool sample with you to be analyized for parasites as well.
While you are waiting on your vet visit, work on making your new iggy as comfy as possible and doing as much research as you can. Ig's are a lot of work, especially rehab igs, but they are definately worth it. You owe it to your new iggy to do all the needed research and make sure you can provide all the care, money and space it requires. And of course you also must find a new home for him if you cannot.
How big is your new iggy?
Make sure your iggy is set up in a tank with plenty of room. If you have it in the cage it was kept in by its neglectful owners then it may not be big enough and you should start making plans immediately to construct a new one, or to give it a room. An adult ig needs a lot of room...if you go with a cage make it at least 8ftL x 5-6ftW x 6ftH. For large adult iguanas, especially males, a small room is best for them.
Keep your ig warm with a basking light that creates a hot spot of 95-110degrees. Branches or other basking decorations should allow your ig to get pretty close (but not close enough to burn himself) to these basking spots. The ambient(overall) temps in the cage can be in the mid to high 80s.
Provide a large water dish that your ig can soak in. He is probably pretty dehydrated so i would give him nice long (30-40min) warm water soaks daily to get his hydration up. Most igs will appreciate these soaks even if they are fully hydrated. You also want to gently mist your ig and his enclosure a few times a day. Makeing sure to allow him and his substrate/decorations to fully dry out in between.
You mentioned that he will only eat from your hand. While this can be tiresome and will need to be fixed, at least he is still eating!!! (which is very good, obviously). Feed him a good varied diet that includes a variety of veggies (collard greens, escarole, endive, mustard greens, dandelion greens are all great staples) there are many lists of food availble online. I believe anapsid.org has one...if not Melissa Kaplins book Iguana's for Dummys has a really good one. The food should be supplemented with a calicum supplement daily, and a multivitamin supplement a couple times a week.
Make sure your ig has access to a UVB light as well.
Get to the vet as soon as possible and keep on working with the little guy. Do as much research as possible!
Good luck 
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