A MIDI controller/keyboard makes life much easier. It's not essential, but pretty darn close to it.
When I shopped for one, one of my problems was choosing the right size. Common are 25, 32, 49, 61 and 88 keys. 88 is full piano size and huge, so this is probably only for people who know what they get. 61 is still huge and probably more than what most hobby producers need, but it's often recommended. A 49 full-size key one was bigger than I thought, but it is a happy compromise between size and number of keys (four octaves without needing to slide them up or down). 49 is also the smallest size that I feel you can comfortably play on with two hands, if you opt for learning some keyboarding. It's not difficult.
Personally, though, I felt it (
M-Audio Keystation 49es) was too bulky for what I wanted it for, so I ended up buying
a M-Audio Axiom AIR Mini 32, which isn't the cheapest model, but it had everything I wanted and was still affordable (around $100/€80). It's great for what I do with it (punch in notes, emulate a kalimba, etc.), and its size is perfect to sit next to a laptop. Also very portable, unlike my 49 keys one.
Read reviews before you buy something. It's better to spend a few extra bucks than buying something twice. (Like I did because I didn't realize how large a 49 keys controller is!)