Just Binged Watched the first Five Seasons. I've got some questions

Hello! Over the last two weeks I have watched the first 5 seasons of community all thanks to Netflix and now looking to watch the 6th season through amazon.

But before I do I've got some questions

1. What was the reasoning behind Chevy Chase and Donald Glover departure? Was it just contract finished and they wanted to go their separate ways or something entirely else? I absolutely learned to love Troy even more so in the later series where as I hated the Pierce. Out of the two Pierce's departure seemed a bit abrupt, he made a very small cameo and then poof, He's gone. Where as Troy's seemed a lot more fleshed out and I completely understood the reasoning behind his character leaving.

2. Is Chang written so we hate him or is it that just me? First season when he was a Spanish teacher I loved him, from then it just felt like he was there for me to hate.

3. HOW THE HELL ARE THEY STILL AT GREENDALE!

4. Where does Abed and Annie get their money from? Annie was quite strict with not taking any hand outs and it's never said that either of them work.

5. on second thought, where do they all get their money from (Apart from Jeff in season 5)