Let me chime in here. I'm an IT guy who has the privilege of doing device testing on a daily basis for a 30,000 seat company. What I will tell you is this - it totally depends on user preference. A tablet generally is acceptable if the software is touch enabled and doesn't require a lot of keyboard entry. As mentioned, there are a lot of Bluetooth and USB keyboards out there if you will need them part-time or infrequently. I have tested a number of tablets, from iPads to Androids to Windows 7 and 8 (RT and Pro.)
Based on the OP's requirements I think that there are plenty of Windows tablets that would be acceptable. The HP Envy X2 is nice in that it can be separated from a laptop into a tablet, and the Surface is also nice in that it has a cover with a keyboard built in available as options. Almost every Windows tablet has a USB port, so that will not be a limitation. There are also convertible tablets that rotate to include a keyboard, but have the advantages of touchscreen if you need it.
As I said, to each their own. Everyone will have their own way to use it and own set of apps to run. If you need Windows, you need Windows. The only other way to accomplish that goal would be through virtualization, which really isn't an option for most people.