You want a laptop that survives until graduation, not just until midterms. Buying a refurbished mid-range machine from a year ago usually gets you a better build quality for the same price as a bottom-tier new model.
July is the sweet spot to hunt for deals before the back-to-school rush peaks. Look for business-grade models, as they are built to last longer and are easier to fix if something goes wrong.
The 0% intro APR is a tool to manage cash flow, not a permanent discount. If you have a balance left when the 15 months are up, the bank will start charging you regular interest on whatever you still owe.