If you are using an iPad as a second screen - you get the same app you have on your mac (obviously, iPad just acts as a second screen: https://support.apple.com/en-us/102597).

If you are using an external keyboard and a mouse with it - you will get the same touch UI, yes.

Many apps are missing many keyboard shortcuts that you may be used to if you’ve used the equivalent on the desktop. You’ll need to keep the iPad screen accessible to tap on UX elements. There’s also the issue that shortcuts that do exist may be hard to discover because there’s no menu bar to look in.