2007-2011, 3.8L, standard transmission, 35" tires: 4.88's, 5.13's if you are going to 37's down the road or playing in the rocks.
Your front D30 is pretty-much limited to 5.13's, with each lower gear ratio (numerically higher), the pinion gets smaller and smaller. Also, 35's will stress your front axle assembly if you use it offroad, you can sleeve and gusset the front axle assembly to correct for that. There is a lot to read about this topic alone!
To attempt to answer your question, typically people add differential lockers at the same time when they regear a sport/x/sahara because it saves on labor cost. If your intent is to go offroading, then a locking differential is a must, they allow the torque to be applied to both wheels (ie. front or rear axle, depending on which are locked), thus both wheels move and will not slip. Videos of 4x4 vehicles climbing impossible obstacles are using differential lockers. A stock sport/x/sahara put in a similar situation would just stay in place, with one tire not rotating (stuck) and the other spinning with no grip (differential applying all of the torque to the tire with no grip). So, basically, you can get automatic lockers that work when they are needed with no driver input (mechanically); selectable lockers that turn on-and-off with driver input (electric, air or cable actuated); and limited slip differentials. Each have their own advantages and disadvantages. There is a ton to write and read about lockers, I'd advise doing research on this topic on the web. Read, read read!!!
IMHO, on a college budget you have two options: first buy the tires - you can drive around in the meantime. You'll be able to get around, but it will take the "good" out of your stock gearing (no more racing on the highway or smoking tires at red lights if you are so inclined) - so regear when you have the first chance! While regearing, if you have the $$$, throw a rear locking differential in. As a college student, you have a lot of $$$ to spend.
Second option: get out while you still can! Jeep mods are a sickness! Lol! Drive your Jeep around stock, invest in your education, get a great job and then blow your wad on your Jeep! IMHO, make sure you're studying to get a good job - with a Jeep you'll need it! lol
Either way, you have a lot of reading to do!