Hi Mary,
I wholeheartedly encourage you to follow Kona's advice! You will need to come up with a unique course ID and section # for the SIS ID fields in Canvas. These probably won't be the same as the actual numbers in your SIS but you'll probably want to trace them back to it sometimes.
We are a High School District and here is what we have been doing.
Here is a Biology course SIS ID
006151610938227LS
006 = School Site identifier
1516 = School Year
109382 = Staff ID of Teacher for the course (This is important to have so each teacher gets their own course)
27L = SIS Course Code for Biology
S = Spring Semester (We use F for Fall)
Within that Biology class we have Sections with the teacher and student enrollments
006151627L1121
006 = School Site identifier
1516 = School Year
27L = SIS Course Code for Biology
1121 = SIS Section ID
We use the Terms in Canvas to automatically conclude the courses at the set dates and to date, we have never deleted or cleared out any of our courses. We will keep them around with all the data in them in the archived (concluded) state for at least 3 years.
Once you make your new courses from your SIS import your teachers can still copy all the content 9or select just some of the content) over to their courses by following the How do I import content from another Canvas course? instructions.
If you follow these guidelines you will be set up for success and avoid many of the pitfalls and bumpy starts that others have run into. You will also have no need to turn on multiple grading periods because you will create new courses at your official grading periods and have perfectly pristine & preserved records should you ever need them 
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