A Floating Nation could be attacked. Could be blown up from the sky or under water, the media will lie about it and nothing will happen.
I think the safest thing to do is to first of all build a successful Nation on the Cyber world/Internet then gradually move to the Sea. The Cyber Nation must be fully developed on Decentralized platforms such as Blockchain and IPFS. It should have an anonymous Biometric for authenticating citizens. Must have Social and Welfare schemes like insurances, mortgage, social security, etc
It should be open source and above 30% automated. Should be possible for Companies to be built on the Cyber Nation more like tokens are created on Ethereum.
The Floating Nation must have good safety measures Survival Pods and small Submarines could be made mandatory in every home on the island just in case of disaster.
I do not think a Floating Nation will destabilize the World. It won't be imposed on anybody. I don't understand the attacks it got initially.