One other note regarding spellling, there is a spell checker when you submit writing so it really isn’t the tutor’s job to correct spelling. If the writer is concerned about spelling, they have the tools already available. If you want to correct spelling, you are more than welcome but it’s not necessary.
Regarding conversations, I think that posted conversations are more likely to get a response than relying on members to request conversations. Having said that, you may have to experiment with times and topics to attract students. I would let any of your German learners or other members you know of who are learning German know when you post a conversation. You can make them friends and then invite friends when posting a conversation.