It depends on your style, I step sequence some things in my songs, but mostly I record midi drum and synths real time. I would suggest picking an inexpensive midi controller like this
It will make playing vsti's easier in my opinion.
Some programs like Reaper have a built in Virtual MIDI Keyboard and you can click it or play it with your computer keyboard. Might be okay for simple things but I would definitely suggest at least getting a small/cheap MIDI keyboard.