All new computers ship with OS 10.11. That's five OS versions after FCP 7 was discontinued. So bear that in mind. Every OS released after the Studio was discontinued, is a step away from full support. THey don't take FCP 7 into consideration in terms of functionality when they do the new OS updates...only FCP-X
Installing it will be tricky...it might not work unless you do a few tricks. I'm going to have to copy and paste Michael_LAX's tips and put them somewhere so I can copy/paste them here.
Note: Compressor, Qmaster, Motion won't work. They stopped functioning at OS 10.9.
FCP won't be fully compatible. A lot of features might work for you...and all the ones you need. But there are reports of features not working, and those reports are random. Multiclip issues, or exporting issues. Log and Transfer...importing...is a biggie. If you don't already have the plugins for L&T from the older camera makers, you can't get them. They don't keep those online anymore. And any NEW cameras released after FCP 7 was canned...won't be supported. Third party converters will be in order.
You might want to look at Premiere Pro from Adobe. It's more FCP like than anything.