Any +1 program is usually 2 additional semesters you will need. So if you need 8 semesters for your undergraduate, you will need 10 total semesters, and need to pay for 10 semesters. Graduate rates will apply once you graduate undergraduate. Depending on what makes sense, it could be useful to delay undergraduate graduation.
Summer sessions are pretty much exactly half of a semester in every way. Half time, half price, half classes (so 2 at a time, double the class time per week per class). Generally people find summer sessions to be easier since you don’t have to juggle as many balls at once, but it can be harder for some courses that get significantly harder when accelerated.
There’s only a week break. It’s the end of the last week in June to the start of the first week in July usually.
Here’s a full academic calendar, more or less:
Spring Semester: January 1 - April 30
Summer 1: May 1 - June 30
Summer 2: July 1 - August 31
Fall Semester: September 1 - December 31
Co-op Calender:
Spring Co-op: January 1 - June 30
Fall Co-op: July 1 - December 31
The summer split is designed to align with co-op so anyone on co-op has the ability to take summer classes before/after if they want. If you don’t need summer classes for a semester, it isn’t uncommon to extend a co-op to cover the full summer, to make an 8 month co-op.