BEFORE YOU GO :
• GUIDEBOOK - get a separate one on Greece, don't count on a Europe one. I suggest ROUGH GUIDE to GREECE -- is detailed and also candid - giving drawbacks as well as pitfalls, good MAPS and backgrounds on famous sites, Greek history, culture, etc etc. Other popular guides are big on color photography and flowery language but very shallow on background (a scandal revealed one famous company gets guides written in NY; no one even goes to the country!). No need to get most recent edition; you can get a 2014-15 edition used on Amazon for $7-8. One BIG advantage -- U can (carefully) Pull sections out from backing & use Duct tape to make a "spine" for each -- voila! a pocket guide-ette. That way u can take just sections u will likely use -- Athens, Peloponnese, Cycladic Islands, Saronic Islands, Crete, & sections on history, language, food etc.
• BUS TRANSPORT - Almost no trains in Greece except a line to Thessaloniki on Eastern side of Mainland. Most transport is by Excellent intercity (KTEL) Bus Networks. These 2 links give the standard timetables & costs AND trip durations for Peloponnese & Attiki / and Delphi & Eastern Mainland: they aren't the official ones, but are easier to read than official & have the same info: http://www.athensguide.com/practicalinfo/busschedulesA.htm http://www.athensguide.com/practicalinfo/busschedulesB.htm
• FERRIES - This website -- https://www.gtp.gr/RoutesForm.asp -- is the most reliable extensive ferry info site. Spend time with it -- it's wonderful. Not only does it give departure/arrival times, but often gives a photo of the vessel, and a little "action map" that shows the route with a moving red line. TIP: By putting in your chosen month (5 = May) and selecting "any" for the date, you can then see ALL available ferry sailings for every day in May. Cool huh. Learn to use this. As for prices you can look them up but it's just as easy to stop in at any ticket agency and inquire about prices. In making choices, the difference is, "cf" (conventional ferry) is the largest (1,000-1800 passengers less fast, and lowest price ticket. "cc" is car-carrying Catamaran - a large-ish vessel (500+ psgr), faster, costs almost 2x as much. "cn" is passenger-only catamaran, 250-400 passengers, smaller, in rough weather can be bouncy. Hydrofoils are only used for islands close to Piraeus/Athens port.
In general, do not try to get by on prep by just what you can get on your phone ... there are too many websites that are just straight promo, not realistic facts u can use.... or just by going on travel forums and asking for "must-see" places; you may get good advice from people who go to greece every year, or live there ..... or you may get uninformed opinion from people who took a 5-day cruise once. You are a student, a lucky one, who has a once-in-a-lifetime opportunity, take it seriously and do some research... it will pay off in wonderful experiences, AND avoidance of costly time-wasting pitfalls.