In response to the original post:
Everything is a "MIDI" keyboard. I don't know of any boards that don't have a MIDI out, let alone a USB Midi out. Suspect what you're talking about is a "controller keyboard" which has no onboard sounds. And yes, even though that's what I use, I don't recommend it for people starting out, as it has a serious learning curve, and requires hauling around additional gear to gigs.
More importantly, when beginning lessons you should think about what direction you want to go with your playing. Do you plan on revolving around piano/electric piano types of playing? Are you possibly practicing to play organ? Or is your goal to be in a band and do the noodly bits? In almost ALL cases (except maybe for organ), I recommend starting out piano style, and since you're taking piano lessons, it seems that's the current area you're in. At this stage, I think feel and piano sounds trounces features. Make sure to get a weighted 88 key keyboard with a good piano sound. Weighted keys train solid muscle movement, and are easier to get good dynamic response for piano styles (be it classical, jazz, rock, or R&B). Even if you're gunning to be a synth weedler (like I tend to do), I personally don't think anything else prepares better for that than conventional piano. The only exception here is organ, that's a whole 'nother beast with a good 500 years of development separate from the piano. In that case, you'll want to practice on a semi-weighted, waterfall key board, and probably have two manuals and foot pedals (though many great jazz and church players don't kick).
Not assuming you're going the organ route, I would suggest picking up a decent "Electric Grand" for beginner practicing. They're not flashy and cool, but they have everything they need for learning piano/keyboard. The modern Casio Privia line is my favorite, though I've heard Roland has some good offerings. I personally don't care for the Yamaha Electric Grands these days, they're not bad, but compared to the Casios, I think the Casio's outclass them in sound and feel at the same price point. With an electric grand, you get a good weighted controller, which is a necessity for practicing dynamics, 88 keys (which you'll need for playing anything 1800s and later, including early R&R), usually passable electric pianos for playing 50s-70s rock/R&B stuff (this is where Yamaha drops the ball IMHO), even a few organs, and basic synth pads/leads to use in a pinch. Electric Grands are usually fairly inexpensive, and include built-in speakers. They even always have MIDI/USB Outs to plug into a computer for controlling other midi stuff down the line. They're built to do piano and do it well, something that other keyboards don't usually do until you get up into the $2500+ range. What they are NOT is a synthesizer or workstation: keyboards where you have hundreds of customizable patches to fill every nich for getting "fiddly" with sound generation. They don't have any customization at all, you press a button, and that's the sound you get.