Research is good and you appear to be on track to making it a personal habit. Good for you!
Here are a few things to consider when buying your Mac:
1) Rarely (if ever) does Apple offer substantial discounts such as holiday, back-to-school or otherwise. If you hope to take advantage of those sort of discounts, you'd best be looking at buying your Mac from a third party such as Costco or Amazon. You'll find that these places may offer limited discounts on "last year's" models that get superseded when newer versions are releases. Older models sold as new will have Apple's full warranty and support, though as you note, you may short yourself a year or so in the long run. Apple does offer discounts for educational purchases, so look into that.
2) An option to paying Apple's full retail price on a new Mac is to purchase from the selection of Macs that Apple lists here: Refurbished Mac Deals - Apple
These Macs are refurbished by Apple, are sold with a full manufacturer warranty and will be priced below that of "new" Macs. These offereings may change daily depending on available stock, but you can specify the features (RAM, storage, etc) and usually find something that works for you.
3) Never buy a used Mac from an unknown seller. Purchase only from reputable resellers. OWC/macsales is one example of reputable reseller. The reasons being that a) not all sellers know how to prep a Mac for resale and b.) a Mac that is not properly prepared may easily become an unusable doorstop leaving you stuck with no recourse.
4) While you may wish to buy a Mac now to carry you through to your college career, be cautious. Your chosen major and the related coursework may dictate your personal computer choice, i.e. Mac or PC. Some coursework may require use of software and apps that don't run on one platform or the other. It may be wise to wait until you have made a determination of school and major and then select the computer that will fit best.
As I said, you appear to be on the right track and are headed for success, wherever your path takes you.
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