No, just download Raspbian (Debian for RaPi) or any other popular distribution on your main computer and copy it to your RaPi’s SD card. Oh and if your mouse “lags” - you can increase your mouse refresh rate in settings.
Also while the setup obviously works and does its job (and is really fun to use) it’s probably not better than a laptop. It’s more of a thing you use because you can…
…anyway, if you already have some of the parts it’s the cheapest you can get, and it is just as practical as a laptop. I already had a pi4 with case, a keyboard and a mouse, so only was missing a portable monitor and a powerbank (but buying a powerbank never is a bad idea anyway).