A good NAS server handles your backups, media, and files for five to ten years if you buy the right hardware upfront. Don't cheap out on a tiny two-bay setup if you know you need four bays down the road. Wait for Cyber Monday drive bundles, and remember that last year's enclosure model usually gets heavy discounts right when the new revision drops with minor tweaks you don't need.
The total setup usually runs around $750 with drives. Spreading that cost out over time keeps cash in your bank account while you get your storage online today.
Keep in mind that a 0% intro APR is a repayment deadline, not free money. If you still have a balance after 15 months, the standard variable interest rate kicks in on whatever is left, making those hard drives much more expensive fast.