M'ath, lajak sash!
To answer your first question, Dothraki is much larger than Valyrian and allows you to build vocabulary from the ~4,000 root words with about a dozen derivational morphologies and compund words.
And apparently this community has been rather slow recently. In my opinion, people just need to post more and add some discussion to this place that goes beyond translating phrases. If you're truly invested in Dothraki, though, I suggest going onto the Dothraki Wiki; read, take notes, and practice using the two memrise courses for the next couple of months until you yourself feel completely comfortable with the full variety of what Dothraki has to offer. If you want someone to talk to while you do these things, I have a Skype that I use regularly to communicate with other members of the community. Send a private message to me, if you want, and I'll give you more info.
Haji, ma ezo chek