Zarthul
I don't know if I would buy a Mac, especially with how often you are going to use excel, I'm not sure if it is still like this but there used to be things/scripts you could only do in Windows (unless you run an emulator of course)
I would recommend an IPAD and then get a regular laptop, probably save you money to boot!
Mac is not a problem at all at Wharton. I had a Windows laptop during the first year, then added an Apple laptop for the second year, and used it happily for all my needs.
The latest Excel for Mac is close to MS Excel in functionality, and definitely enough for the classwork. However, you might need a Windows laptop for situations where you would need very advanced MS Excel skills: say, if you recruit for some entry level PE jobs, sometimes the firms would ask candidates to build an LBO model, and they would usually provide Windows PCs for that so you would need that skill to be competitive.
In all other situations there is no disadvantage to using a Mac whatsoever.