Yes you can buy fractions, but a VIVA Crown will only be really useful when you have a whole crown. Then you can 'register' a crown, so it gets officially and you can use it. If you now have one crown and you have a business (in real life, that is not minting VIVA), you are permitted to mint VIVA with the Treasury Rights.
I can't tell you how exactely it works, for that you maybe need to read the whitepaper.
Come on cryptos are real life!! And thank you for your answer i'll take your word until i'm interested enough to read the white paper!