Hey frankie, I'm gonna risk the cheeky answer and just say ride 4 or 5 times a week for a total of 7-10 hours. A little more if you plan on doing any entry level racing. Include some hills for built in intensity, if possible ride with some friends who can challenge you once in awhile, and try one ride a week of at least 3 hours to help build endurance. If you have been somewhat inactive, just riding for an hour or two a few times a week will show you quite a bit of improvement.
Consistent, moderate intensity riding (with sprinklings of high efforts) is usually all it takes to get in good riding shape, and depending on genetics maybe even entry level racing shape. IMO structured plans are for folks who are hitting plateus, have specific racing or performance goals, etc. Just ride as much as you can and enjoy your break from school. As far as cross training do whatever you want. I have done some running, weight trained for years, tons of different martial arts - for me the only activities that translated into strength on the bike, were activities (wait for it)... on the bike.
