Can I use a Keyboard?
In short, yes, a keyboard will be fine—I use one myself! Acoustic pianos are wonderful instruments, but do have some disadvantages when compared to their digital counterparts—one obvious disadvantage (as I’ve already mentioned in another article), being that acoustics don't have volume controls or headphone connectors, so your neighbours or housemates might not approve of your shiny new piano! With a keyboard/digital piano, you can just plug in some 'phones and play whatever you want, whenever you want without disturbing anyone. (I should point out that some acoustic uprights have a ‘practice’ pedal which when pressed down, places a piece of felt in-between the piano’s strings and hammers, thereby muffling and reducing the volume of the piano’s sound; therefore, if you go for an acoustic this could be an option for late night practising, but test first to see if it meets your requiements).
Acoustics do tend to also be more expensive than their digital cousins and require more maintenance (for example, regular tuning). They are of course, also less portable than keyboards and some digital pianos (full cabinet digital models score closer to acoustics pianos in this respect as they are built with large cabinets to look more like acoustic pianos, and are therefore not designed to be lugged around every day!). However, I’m guessing that portability isn’t going to be high on the priority list for those just starting out!
The keyboard I have is a MIDI (Musical Instrument Digital Interface) controller—simply put, it doesn’t have any build-in speakers and doesn’t include any sounds of its own. It hooks up (via MIDI) to my PC, which runs DAW (Digital Audio Workstation) software. It is within this software that I run my virtual piano instrument (for those who are interested, I use Cakewalk Sonar as my DAW, and primarily use the Alicia’s Keys virtual piano which is part of Native Instrument’s excellent Komplete Ultimate suite). So when I play the keyboard, it is the PC itself that produces the sound. However, you don’t need all of this! I have this set-up because I like to write, arrange and record my own material and so have built a home project-studio of sorts over the years… long before I decided to try my hand at actually learning to play the piano. If you want to go down the ‘headphones so I can play all night’ route (please, don’t actually play all night, remember to get some sleep, it’s important!!), all you really need is a digital piano or a keyboard (with it’s own sounds/speakers).
I would say that 61 keys is the minumum number of keys your keyboard should have—any fewer (say 49) will likely feel too limiting, especially when playing certain passages or playing with 2 hands. If you can stretch to 88 keys then all the better, as that's standard for a piano.
A Weighting Game
I would also definitely recommend—if you’re looking to purchase a keyboard—that you get one with fully weighted keys. These will be much closer to the feel of a real piano’s keys. One thing I don’t like about my keyboard is that its keys aren’t weighted and they feel kind of 'cheap'. When I get a new ‘board, it will most certainly have graded, fully-weighted keys. There are various types of weighting for the keys on a keyboard, for example: non-weighted, semi-weighted and fully-weighted/hammer action keys. There are also ‘graded’ fully-weighted/hammer action keys which further emulate the feel of a piano (with more resistance at the lower-end than at the upper-end of the keyboard). If you already own a non-weighed keyboard and don’t want (or don’t have the cash) to buy another one just yet, I would say it’s fine to start off with it (just try to make sure it has at least 61 keys. If you really start to get serious about your learning/playing, you can always get a (graded) fully-weighed keyboard later (and you’ll probably want to, as you’ll eventually want to get used to the ‘feel’ of a real piano). So, in short, it would be better to start off with a fully-weighted keyboard, but it’s not the end of the world if you can’t!
Pedal to the Metal
If you're going down the keyboad route, do yourself a favour and grab a sustain pedal! A sus-pedal will allow your keyboard to better mimic the behaviour of a real piano, and bring more expression to your playing—and you should be able to pick up one relatively cheaply.
Play Before You Pay!
I would always recommend actually trying out various keyboard/piano models and speaking with a piano expert before parting with your hard-earned cash. I know, in this day and age people just want to order online as it’s so convenient. But you’ll be using this keyboard/piano a lot and I definitely think you’ll want to try it out before splashing the cash (you can always try the keyboard somewhere, then buy online if it gets you a cheaper deal).
Now, I’m no expert on pianos—I’m simply someone who, like you, would like to learn to play one better. I'm also someone who wanted to share the knowledge I do have (and have learned), as well as describe my own set-up and show you that (in my opinion), a budget keyboard is fine to get started—that you absolutely do not need to spend huge amounts of money to get off the ground (and you probably won’t want to part with too much of your hard-earned cash anyway, until you know for sure that learning to play the piano is definitively for you).
I really hope you found this interesting and useful! As always, good luck, you can do it!