I spent the first month of my learning process solely using pinyin. I didn't even expect to touch the characters until months down the road, because my primary desire was to jump-start my speaking skills. However, I picked up the language relative quickly (I have a lot of time to burn), and at about the one month mark I realized I would improve much faster if I learned the reading and writing, especially considering I am in America and my access to native speakers is limited to over-the-phone or computer interactions. The pinyin was an absolute necessity in learning and developing my tones, as well as consistently making and correcting my mistakes when I had the chance to talk, and it was also an aid when learning those initial thousand-or-so characters, in that I already knew the words, I just had to associate the sounds and pinyin writing with the characters. I'm currently three months in and I've downed several grammar guides, six short stories, and plenty of online resources. I'd say that pinyin is an essential training wheel, or at least for me it was. When to take it off, however, is completely up to the person riding the bike; and I'm sure some may not even need it at all, but I doubt if those people are even anywhere near the majority.

If you don’t know pinyin, learning characters and sentences will be very difficult. Definitely best to learn pinyin first. How will you remember them otherwise? Just remembering the sound is very difficult for a beginner, especially tones.