Errors in Hiragana 2
I've just started using the Duolingo Japanese course. I know it's still in beta. In the first lesson of Hiragana 2 there are letters in the "match them" blocks that have not yet been covered in the lessons. It's not until lessen 2 and 3 that these are introduced.
There isn't the Japanese course on memrise. There are many vocabulary lists (mostly, users create lists to help them remember the words from their textbooks). I stopped using it a while ago, so maybe my info isn't up-to-date but in my experience, there were hardly any sentences and no grammar.
If you want to learn the kana, there also are tinycards decks for that. But I like the way in which Duolingo teaches you kana which you can then immediately use for words (like い and ち which then make いち).
I haven't yet looked at Memrise's Japanese program. Went ahead and downvoted myself:)
I started out (prior to attending in school) by familiarizing myself with the sounds and basic structure using an audio tape/book combination (I know, I'm dating myself). I would suggest that you start with something established. It seems like people on this forum seem to prefer either the 'Genki' series or the 'Minna no Nihongo' series. I don't think it matters as much which one you start with, as long as you start when you are still passionate about learning the language.
I'm sure that other (more recent learners) can answer your questions better about study materials. YouTube has a few good options too!