1. I've never automated my workers, but presumably if you conduct your wars and trading wisely, you may be able to win on chieftain with it automated. Warlord too. If you haven't read Cracker opening moves - you should. You will see how poorly the AI anticipates its builds. If you have a lot of opponents on chieftain that might doom you - the AI gangs up on the human much of the time. You need these advantages to win.
2. Basic rule in despotism is to mine green and irrigate brown because of the despotism penalty. Usually you work flat tiles first (before hills and mines) because you can improve tiles quicker. Also, usually, you do not chop forests and you stay away from jungle unless you have a solid base. There may be exceptions.
3. Yes, you may improve squares outside of your city radius if you plan to put down another city to capture it or need a road to connect things - but ultimately you'll want those improvements under your control to capitalize off them. This is one of those areas the AI is so bad at. If it is outside the side radius, the AI ignores it like it doesn't exist.
4. Yes to Roads - but if you have a long stretch outside your control, remember that the AI and barbarians can use them for free - though barbarians are more likely to pillage them than use them. Definitely road inside your empire - basic rules is to never leave a tile without roading. Again, there may be an exception to the rule, but rarely. The road gives you the reduced movement and +1gpt if you work the tile.
5. Working flat green and brown is a good start. There are usually plenty of them to keep you busy for a while. Then I move on to forests and hills. Last are mountains and jungle. The exception is if it has a luxury or resource you need, and then you road it regardless (but with consideration). Remember that a settler will clear a patch of jungle and build a road when it settles. I don't know that I would let that dominate my city site choice, but it is a good thing to keep in mind.
6. NEVER disband workers. Depending on your style of play, you may join them to a city to add a citizen. I rarely do this - I keep my workers from the beginning to the end of the game. There is usually plenty of work for them to do. But if you are inclined, then send them a city and join them so they become a citizen again. Workers are like citizens at large. I can't image a situation where all of my cities are at max population and couldn't use another citizen. If that is truly the case, build a new city for a gold or science farm and dump your workers there.
7. You probably hit the disband command on the keyboard or something. I am not aware that the computer ever prompts you disband something on its own? Not sure on that. If they don't have tiles to work, they just stand around and ask for new orders (I believe). I don't automate, but on the few times I have automated pollution control, that is my recollection. Might want to listen to someone else on this.
8. 40 workers at 1500 AD doesn't say much. City count and tech is what matters. Do you have rails yet? How many cities do you have? Are you planning on conquering more that will need improvements - such as changing those useless mines around corrupt cities to irrigation to build gold/science farms? Honestly I have rarely had a game where I have considered everything done and my workers to have no future value. That might be my defect. I have NEVER considered disbanding a worker.