I am not sure version 18 would a good choice at this time, it has just been released and has no bug fix releases against it yet. Given the other complications in your upgrade, OS upgrade and multi-version jump, I don't think you want to add a brand new version to the mix. Postgres 17 on the other hand has been out a year and has had 6 bug/security fixes. It is probably a more stable target version.
I hear your concern, but I'm pretty confident in v18. Additionally, they are on version 11 (eleven!) so obviously major upgrades are a rare thing, so might as well buy themselves another year. :)
