I think you will get most bang for your buck and higher uptime first by getting a better, dedicated hosting provider within NJ rather than getting a backup. Most vendors were still up at NY4 even when Hurricane Sandy knocked out most of Manhattan. And the WAN network between your main and backup is likely more unreliable than the moving pieces within a data center. And your uptime will be nearly on parity with the matching engine if you're in the same facility - it's arguably better that you have only 99% uptime but your downtime is in sync with your broker ISV's order execution gateway or market order gateway, than 99.999% uptime that is out of sync with gateways that you need to reach.
The problem with backups and redundancy is that it sounds good in principle, but they introduce complexity that can be worse if you don't spend the effort on setting up a good recovery process. And recovery is a lot more challenging than backup. For instance:
- How does your backup application know the exact residual position and orders at the time your main one failed? Drop copy? Asynchronous messaging between them?
- What if your main application is actually still running but just unreachable?