I want to buy a chromatic harmonica and I've never had one before nor played one. As a beginner, what should I look for in a chromatic harmonica?
Are there certain features I should look for or avoid?
I would suggest the best 12 hole chromatic that you can afford. 12 holes gives you 3 full octaves. Each extra set of 4 gives you another octave.
Based on your reputation you probably are already versed in musical theory and reading. The slide gives you access to all 12 notes of an octave, in a fairly logical layout. Once you get the hang of activating only one reed at a time, your music background will give you the rest. Handling keys, sharps, flats, etc is as easy as on a keyboard, if not easier.
A better quality harmonica will be easier to blow and suck (more responsive reeds, tighter fit). Beyond that I don't think there are many features that distinguish one general purpose chromatic from another.
I bought a Honner Educator 10 ($50) Not quite the full 3 octaves, but adequate for most music. It's not bad, but the Suzuki diatonic (Bluesmaster) that I bought about the same time is much easier to use (apart from the diatonic/chromatic difference).
If you have other features in mind, you might add those to your question.
In my limited experience, the chromatic is better for general melody playing. But for chords, blues and most harmonica special effects, the diatonic is better. Diatonics are also cheaper for comparable quality - until you start buying a diatonic for each key.
A standard diatonic harmonica plays in only 1 key. A chromatic harmonica has a button on the side that gives access to more notes, so you can play any note.
If its your first harmonica, a standard may be easier to learn on because there is a specific pattern of sucks and blows that is repeated on other standard keyed harmonicas to run through the scale.
Most chromatics are in C so you need to "learn" the scale for every key.