How can I use a vanity address as my main address 
This is a bad idea.
Satoshi himself explained that for increased security and privacy you should use a new bitcoin address for every transaction.
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As an additional firewall, a new key pair should be used for each transaction
True that reusing addresses does harm your privacy and slightly harm your security, it is not advised.
But AFAIK, it still doesn't pose any risk to your bitcoin unless there are problems in your transaction signatures or ECDSA algorithm, or those on-chain gambling sites would have been gone.
It's just another layer of protection if one of the hashing functions goes down. You could still use the state of the Blockchain for all the addresses that have never issued a transaction. There's no known way of compromising a wallet just because it has been used to send coins.