Yea okay. I actually decided against an iMac now. However i do not know how to build a pc.
Actually i planned to buy a Lenovo thinkcentre in the small form Factor size.
Do you know if thats okay?
Simple things to look for in your case:
Processor: i5 or i7. You don't really need anything more powerful than an i5 if you're not completely into the editing side of things.
RAM/Memory: 8GB or more. 8GB should be fine for you.
Storage: whatever you need. 500GB, 1TB+ or more.
I'm not sure about the specs you're looking at on the Lenovo Thinkcentre but they have different SKUs to choose from each with different specifications.
I personally don't recommend branded systems to my customers if they're planning on future proofing (they can be harder to upgrade & fairly limited even if so) but for business related use, branded is the way to go.
If you do still find you're having trouble editing for whatever reason even on a more powerful processor, you can try a clip replacement trick.