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
Exactly what I was going to say , he also wrote that on Bitcoin Core Receiving payments Tab ...
Beside if you are looking to import one of those adresses to your wallet , it depends on what wallet mate , not all of them allow to import new adresses , like Electrum for example I guess you can import but it become seedless so you can't get it back from the seed . So watch out