With one exception, described below, the E403 would be a great starter keyboard to learn, with the understanding that it only has 61 keys, as opposed to the 76 weighted ones that I think would be the minimum for a real pianist, or the 88 insisted on by some purists. A couple years ago I was in the same situation as you and got a similar but slightly more expensive board (still only $300) called the PSR-K1, and although it has limitations I love it. I am sure that if I was a keyboard player I would want something better, but as a guitarist I have spent many hours with the K1 and these days almost everything I write begins there.
IMPORTANT .... The one negative thing about the E403 is I think that it will not save to a MIDI file directly, which may or not be something you want to do. Most of the cheapy Yamaha boards have internal multi-channel recording features and autoaccompaniment features that let you record what you are doing in the same way as audio recording except the result is MIDI data in USER songs that can be played back on the keyboard. If I want to send a MIDI file to another Yamaha user, my K1 allows me to save a USER song as MIDI on a flash memory card and move it to my PC that way, instead of the going through the trouble of connecting the board to a PC running sequencing software and recording it that way. Its not a big deal if you don't plan on exchanging files that way, especially considering that the MIDI files put out by cheapy Yamahas do not play well on other, non-Yamaha MIDI tone generators.
Ii you are not in a hurry to buy, I recommend having a look at the Casio boards as well - some folk prefer them, some don't. Also, at the time I bought my PSR-K1, Price Club had Yamaha DGX boards on site that one could play to get an idea of the sound quality before buying on line.
Tom