I read some time ago in some blog that 1000 is where you want to be to keep from disappearing. Once it gets below 1000 there's no coming back from that. I don't know how true that is since I haven't started yet, but it's given me a guidline to go by. Unless that blog was totally wrong, then do correct me.
The same blog said to try to make 1000tk per hour at least to keep that score from dropping below 1000 which makes sense since it's all figured out by hourly earnings.
And this is probably more than you wanted to needed to know.....lol