Hello
Adding PvP skills to each class is the direct solution to address balance. Regular skill book will not be usable, thereby making it easier to address specific classes without needing to modify hundreds of skills. It is also likely that set skills would also be blocked in such PvP scenarios.
Regarding rewards: Cards are given on different droprates based on your result. In siege this will be dependant on if you win, draw or lose.
Siege times are intended to be one evening slot only per time zone, we don't plan to add another slot, but can look at adjust the current evening times if it's better for the community.
Greetings