".... should I do with the break go disc or should I stay with the dums?"
>>> Because I'm guessing that you are only starting to 'hop up' your Stang, I'd suggest you stay with the drum system for now.
I'm also guessing that money doesn't grow on trees at your house. So considering that your car is almost 15 years old now, I'd suggest that you inspect your current four brakes for proper shoe & retaining springs operation/condition, drum condition, condition of the flex lines, and bleed all four corners until they flow clean.
If you don't have one yet, I'd highly suggest you invest in a repair book, such as Chilton's Repair Manual. Not only will it help you during your brake system inspection/tuneup, but it will assist you dramatically during upcoming inspections, tune ups & repairs.
"...and does the 5 lug conversion do anyting beside give you more rims to choice from."
>>> 5-lug hubs are stronger than a 4-lug hub, however again, at this point in your game, I'd suggest you not bother with it just yet, rather put the $$ to better use ensuring that the car is up to the task of accepting more power; one step at a time.
One of the first steps you'll want to take will be to ensure that your car is safe and capable to handle added power..... Start with giving it a thorough tune-up.
a) Change all the fluids & filters: air filter, motor oil & filter, gas filter, antifreeze, trans fluid, rearend lube, powersteering fluid and as mentioned earlier bleed the brake system. Correct any major leaks, if you have any small leaks, check the levels weekly & keep the fluid level up. No brake fluid leaks are allowed.
b) Do all four tires have at least 1/2 of their tread? If not, step up and get some better tires. Nothing fancy now; they can be used tires. They just need to have at least >50% tread.
c) Check the front end ball joints, tie-rod ends, and remaining steering linkage. Sometimes front-end alignment shops will do a free inspection of your car. Have them do the inspection while explaining/showing you how & why things need work. Then tell them, "Thank you. Now I know what it needs. I may be back next week." Then leave. You can now decide what work you can do yourself or what you'd rather have them do - because of a lack of torches, air tools, etc.
d) Is the current exhaust system leak-free? If not, then repair as necessary.
e) New sparkplugs (gapped correctly) and sparkplug wires as well as a new distributor cap and rotor would also be good.
f) Any cracked windows? Replace them with used or new windows.
As you can probably tell, I'm simply trying to encourage you to upgrade ALL aspects & systems of your car to better make it road-worthy. Once you've gotten the above list completed, you will be more familiar with your car and it's overall condition that it is in. Only then would I recommend that you begin thinking about & budgeting toward performance improvements. You don't want to simply start throwing hot rod parts on it without knowing if it can take it.
Your book will tell you how to do a compression test. Buy or borrow a tester from the school shop and do the test on all cylinders. The test results will tell you just what shape your engine is in - if it will take "hot rodding" or if it's old & tired & about to check out....
Ok, let's assume that you've done all of the above list and the compression test indicated that the engine is fine. So what improvements should you start with? The first improvement I'd suggest you plan would be with a set of aftermarket shorty headers bolted to an X or H pipe leading out to dual exhaust. They'll be a kick-in-your-pants in the performance area & with the excellent tune up you already put on the car, they'll sound GREAT!
Meanwhile, as a reward to yourself for completely all your school homework every night, read up on your mustang, like sites as this one, magazines, etc. to give you ideas what others have done and what you might like to do with your car as your wrenching abilities, confidence, spending money, etc. grow.... No, I didn't lay out a complicated list of tasks for ya; just take it one step at a time and it'll be fine!