Can you tell what characters are valid for a domain-name, the maximm and minimum size, and any other rules that need to be followed?
There is no specific rule to be followed but you should choose domain such that it is easy to remember.
You mean all key-board characters, like #$* etc are allowed, along with numbers and alphabets?
Some of them are allowed but its not a good idea to use them.
i think any ascii character can be use, but there are some restriction, like -xxx.com (you put dash as the first character).
now with internationalized domain name (IDN), any weird character can be use.
You just need to make sure people can remember it.
the rule is simple enough that anything except special characters