I would advise against an all in one.
Not always upgradable and not easy to repair.
My friend has older MSI all in one.
The CPU fan went out.
Impossible to replace.
He eventually kluged another fan to get it going.
With a desktop, the CPU fan is a 15min job with 10's if not 100's of cooler options.
Sander is correct, I built an I7-5820K in summer 2015 for $1500 including 32GB, a hi-end case, and water-cooling.
An I7-4790K is more like $700-$800 and will run rings around the MSI all in one.