Visa

I’m confused about how exactly the visa situation works. I know I can only stay for 90 days out of a 6 month period but I’ve seen some posts that say “in a calendar year”. Thus, my question is what if I stay for October, November, and December, then January through March. It’s more than 90 days but would that time period restart with the new calendar year? (Fyi, I’m trying to stay in Switzerland.)

Other possibilities I’ve though about but which I’m not sure are possible are staying in Switzerland for 89 days then become a student and getting a student visa.

I’m a non-US citizen holding a Schengen VISA issued by Germany. I’m flying from New York to Munich the first stop. Can I depart from Brussels back to New York?

My plan was to stay mainly in Germany but thought if I stop by Brussels why not fly from there so I don’t have to travel back to the first stop.

I am applying for a student visa March-end of August. The best flight I have found to far is on Orbitz. for $757 March 3-September 15.
I have found something cheaper to London but they ryanair flights to Perugia don’t match up on my arrival date.

Has anyone found something better? I need to get to Perugia so Rome is closest.
Secondly, can anyone help me wout with one way flights? I could end up enrollong in more classes to extend my stay permit. The San Francisco consulate says I need round trip flight reservations, so do those appyling for a visa permit never get one way tickets?

Do I need one?