Can I use a 7200 rpm hdd in this device?

So in your mind RPM is the ticket for fast data. We'll in years past that was often the case over time newer recording methods have on the most part altered things. So its more important to scrub through the data sheets to be sure here.

The other factor is heat! High RPM drives tend to run hotter! So tight systems like the iMac 21.5" and the Mac Mini can encounter heat issues. So I don't recommend them here. Instead I would go with a SSD which runs much cooler and consumes less power.

So what to do?? I would go with a SSD for the boot drive (to gain the speed you want without the high heat) and put in larger HD drive as your data storage drive.

As an example I have a mini at home which now has 2 - 2 TB SSD's for my media server. I also took out the HD's I had installed and placed them into an external Thunderbolt OWC case. So my Mac Mini can run cooler. I'm not recommending you go this far I just want to give you some ideas on what is possible.