Dell sells rebadged APC rack and UPS equipment. I tend to think APC manufacture some of the nicest racks on the market. Since your order appears to contain Dell servers, storage and networking, I'm sure they would be interested in providing the appropriate rack and battery. Looking at the quantity of systems, you may even have some pricing leverage.
In short, work with your Dell vendor or sales representative.
Outside of that, here's a primer on racks. And the power/UPS situation is going to depend a lot on your infrastructure and facility's capabilities (e.g. Do you have a generator? What are the runtime requirements? Are you planning a dedicated circuit?)