I started Chinese blog for practicing for writing Chinese.
I think difficulty in Chinese for Japanese is Chinese Kanji and Pinyin. Pinyin is like Romaji for Japanese. We Japanese know Japanese Kanji reading in Japanese, and we tend to read Chinese kanji in Japanese. So we feel difficult to memorize both Chinese Kanji and Pinyin. If we don't know Pinyin, we can't type in Chinese. So I often search Pinyin on web.
Speaking of Kanji, Japanese Kanji is different from Chinese. On the top of that, Chinese kanji using in Taiwan is different from in Beijing. For Taiwan is Traditional Chinese, and for Beijing is Simplified Chinese. It's difficult for Japanese to read Simplified Chinese, because it's too simplified. It's easy relatively for Japanese to read Traditional Chinese, because we can recognize meaning by shape of Traditional Chinese. So I use Traditional Chinese for my Chinese blog and tweeting in Chinese.
By the way, my aim to studying Chinese is writing grumble in Chinese. I reached this level in English, but it's difficult in Chinese now. I continue writing in Chinese even if the sentence is too short.