Smallest I've gone is mini-tower, and I have to keep sides off and my hdd outside the case to cope with overheating.
Are you in an equatorial country?
It gets pretty hot here, believe it or not.
How small is a small form factor? We have some teeny little boxes in work but I think they are mostly used to access servers over a remote desktop connection.
Can you just stick the SSD in there dangling around? Don't think I ever fixed mine in properly, it's just sitting bottom of the case.
Depends on the age and manufacturer.
The Ultra SFFs have no expansion and are the type of things you can VESA mount. I've got one at work (HP Elite Desk 800 G2 Mini) and it's a nice little unit, Core i7 6700, 8GB, 240GB SSD.
Normal SFFs usually have a couple of half height PCI/PCI-E slots. Maybe space for another drive in there. But not much room for expansion. Ideal for an office environment.
Are gaming enthusiasts a problem where you work?
Just stupid bloated spreadsheets that still sit "Calculating" for far too long even with that spec.
Been there, done that. I only have a Core i5 laptop for work, but quickly found 4GB of RAM insufficient and needed the 8GB. Sometimes when you're manipulating spreadsheets with several hundred thousand rows, and some complex calculations and a pivot or two, Excel can really grind and chew up plenty of memory. Especially if you have several different sheets open at once...
I know spreadsheets are essential for many business functions, in fact these days there are plenty of tools (the software sort as well as the staff variety) that won't work without them, but back when I was in a humble team of DBAs, we often wondered whether spreadsheets weren't being stretched beyond their useful capabilities. To be fair, this was mainly just after we'd been emailed an epistle by some "scrum-master" who had managed to embed powerpoint presentations into every cell.
IT managers love Excel because it makes them feel as though they are "proper" IT people.