As a consultant, I deployed and maintained models of nearly every brand of network gear under real-world conditions; as a technical writer I obsessively test them, and listen to readers’ concerns to make sure I’m testing the right things.
If you’re happy with your Wi-Fi, you don’t need a new router—it’s as simple as that.
Later versions of Windows (8.1 & 10) already support SHA-2 per default, however if you're running Windows 7 you will need to have the latest updates installed.
If you still encounter issues after updating please let us know in the comments or in our forums If you are running Windows 7 you'll need to install the Microsoft Security Advisory 3033929 to make your system support SHA-2 Code Signing.
In the real world, AC1900 means pretty much the same thing AC1750 does—a dual-band router with one 2.4 GHz radio and one 5 GHz radio, each supporting up to three spatial streams.