Get a desktop or laptop set up for financial modeling at home?

To each his own. There are people who can't stand doing Excel on laptops and absolutely need a big screen and a nice keyboard, so for them a desktop makes more sense perhaps.

But I would say that the general rule is that desktop computer nowadays are only the way to go for video games and multimedia stuff like video editing or Photoshop.

For Microsoft Office type of work a laptop does the trick IMO. And it's a formerly avid desktop computers user that tells you that. Condition though is that you get a relatively powerful computer with a 17 inch screen. Worst case you may still buy a separate screen (like 23'') and/or keyboard to plug in your laptop if you think you need that extra comfort. The price difference between a laptop and a desktop (of equivalent power) has been ever narrowing so I think for most people the laptop makes more sense. You may get sth like a Dell Inspiron 17'' that will be handy to read ebooks as well (if you plan to pass the CFA for example), or anything equivalent.

But it's a matter of preference. If: - you have enough space in your flat - you are absolutely sure you will never ever be willing to use your computer in another location - you find desktop computers more comfortable to use - you won't need to use your computer in your bed or in your sofa Then you may rather go for a desktop.