Are there any important things to do or check before moving a dApp from Ghostnet to Mainnet?
I would say it always depends on the specific use case. E.g. is it a DeFi protocol? Then you might want to have your contracts audited too before moving to mainnet.
If there is a contract bug it is not possible to just fix it, you need to migrate. Besides that if the application is well tested on Ghostnet and even covered with unit/integration tests you are probably good to go.