I can probably get you started:
1. SE10, pull up the change request. highlight the task, hit the truck icon, then highlight the request and hit the truck.
2. most tasks would be created automatically when you make a config/tech change, for example if you change config in SPRO. I don’t know of a maximum number of tasks.
3. A change request is the parent of the task. A task is a single change, for example a new order type. You can have many different tasks under one change request. Related tasks should be logically grouped together in the same request. You must release all tasks before a request can be released.
4. ?? depends on the specific change. Generally speaking most config (SPRO) comes under customizing, technical changes (program changes, SE38, etc) under workbench.
5. ?? depends on your system architecture. Generally, you need at least a Development system, a QA system and PROD. Often you need many more systems, data load, regression, …etc.