I've been looking to learn piano for a while. I'd like to get a cheap keyboard that I can hook up to my 13" MBP(I've got some pricey headphones I may as well put to good use).
Would it be best to get one with 88 keys like an acoustic piano? I've heard you don't need that many but I'm not totally sure why. Won't allot of music have notes that I won't be able to play?
Somewhere around $100? I don't want to put down too much dough on something I'm not sure if i'll continue.
At that price point and for your purposes I'd say "it does not matter" All of them are not very good and you will need to upgrade soon. At that price point Casio is the brand.
Are you planning to learn
piano or just keyboarding. At the beginning there is not much difference as first you need to learn just the notes on the grand staff and how to find them on the keys. But very soon you will want to be able to control dynamics (loud and soft) and you will want an expressive keyboard. For
piano the lowest price entry level keyboard is the Casio CDP100 but the Casio PX130 is better for not much more. All piano keyboards have weighted "hammer action" keys. The cheap $100 broads have just springs under the keys.
There is little point connecting it to the computer unless you want to record or play software virtual instruments. The keyboard's built-in sound will be fine. That said almost all keyboard will connect to a computer. It is a near universal feature
If you do get serious the $100 class keyboard will need to be upgraded in about 6 months. If you make the same rate of progress that most people do. You wil likley start looking for an upgrade after three months
What you need is a good "method book". Those utube and garage band lessons are bunk. Don't waste you time. They just don't have enough content. For $20 or less you buy a copy of Alfred's all in one adult beginner book. Any music store or Amazon will have a copy. The books optionally comes with a DVD and CD. Those are worth the $10 extra bucks
http://www.amazon.com/Adult-All-One-Course-Lesson-Theory-Technic/dp/0882848186/ref=pd_bxgy_b_text_b
Better place to ask this question is at the "synth and keyboard forum here:
http://www.pianoworld.com/forum/
Lots of people there. But be prepared to hear advice like "get a teacher" and "get a keyboard with decent piano-like key action"