which is best

you don't even need a midi keyboard but its much easier to try some sounds out, find some tunes out etc. If you want to have a good and flexibel homestudio you need an audio interface + mixer (to records vocals, guitars etc), a midi keyboard, maybe something like a mpc/ m-audio trigger finger or nanopad to easily make some drumlines(but a good midi keyboard can do the same work;) ) and something to control your the internal mixer of your daw. I got two behringer bcf's because you don't need so setup everything again after changing the song you are working on. AND the importants thing you need: good speakers! When you are able to make exactly what you want with your daw then you need to hear your songs in a way you normaly dont hear music. Just search for some selfmade tracks on youtube and you will hear that many people are making mistakes like: instument 1 is to loud, vocals are to unclear and so on. When you got a good sound system you will hear such things early enough to correct them. Anyway its always a question of taste (and of course: money) You can even make a unbelievable istrumental track with a casette recorder and your mouth soo ;)

Whatever is available is okay. But for me guitars/keyboards and different type of instrument is the best because it will help you improve you skill and some are more handy and it feels better when you are the one playing the music you like with your own version.

what ever it may be pc or work station. but the real enjoyement is felt only when we became calm and go deep into the music