If Staples said it would work then you can take that to the bank. Seriously, they haven't got the slightest idea what they are talking about. Firstly, no, the motherboard from a different model will not fit. And it is not the motherboard you want to swap I think it may be the hard drive.
You can transfer your data to the new laptop but programs like Office 365 will have to be reinstalled but you have a license to do that.
Trying to put hardware from an old laptop to a new one is like taking a used card and trying to put the engine with 100,000 miles into a new car. Generally can't be done but why would you want to?