If somehow hackers gain a momental access to all the wallets on the server and obtain a copy, most of the users could be sent messages through sms asking them to change the password before the hackers would bruteforce a single one.
I am wondering what is the best method to encrypt individual accounts within a wallet...
Yes we are hopeless, we are trying to understand your logic, first off can't encrypt individual accounts within wallet. Second SSL is good but if your not securing the server well, you could still be hacked. Third you can't brute force bcrypt it is impossible no computer can do that. The problem would be users lossing there password or the hacker copying the wallet.dat file.