Setting up a shop is costly at first but a good way of getting tons of DCD's!
Either buying the whole stock of one person's stock and then selling them for a few more DCD's (not sure if this is allowed, sincere apologies if it isn't, if it isn't I WON'T do it!).
Also a good way of getting money from making shops is finding what people want. For example mending books (but plz don't afk fish farm!), diamonds (use fortune and get tons, that's what peeps want!), emeralds & iron (make an iron farm), etc.
There should be more quests though, as some people have probably finished most/all of them by now.
You should also do the mob arena in teams, so you have a higher chance of getting to better waves.
-Limo (my two cents!)