I will need an L67 lower end and an L36 upper end. - Why?
The throttle body off of an F-body. - Why?
And will probably have to have a transmission built for it. - Why? You are a student. Save your money and run a stock 3800 SC S2 4T65E-HD.
So which computer would I need? - Will need to work with your tranny. If the 4T65E-HD depends on the year of your transmission.
ODII but would it still need programming for the transmission? - Yes
How much of the original donor cars wire harness will I have to pull (or should I have a harness made) - Entire donor engine harness either way if you build your own or have it built - shameless self promotion - http://reddevilriver.com
Best engine mounts to get (or how to make my own) - If you don't have the equipment to make your own it is better to buy them. If you are asking then I am thinking purchasing is the best way to go.
Is running air conditioning possible and what will I need? - Yes - Compressor and pressure transducer from the 3800 donor - custom lines to the Fiero firewall bulkhead - You will have to convert to R134a if you haven't already
I'd like to have cruise control as well so do I need the donor or can the fieros work? - The electro-vacuum cruise on the Fiero sucks. Use the digital cruise from the 3800.
[This message has been edited by phonedawgz (edited 09-13-2014).]