as per my knowledge if you have registered the reporting centre for the first round and havent withdrawl the fees then you dont have to pay again you can check the official website information 

Yes once you are allotted seaTs in wbjee, you can either pay fees and reserve seat else yiu can opt for another round of counselling.

Approximately 5000 rs ro be paid for government or state f aided institute for allotment of seats. 

More information on wbjee seat allotment below. 

https://engineering.careers360.com/articles/wbjee-counselling