The thing that makes me wonder about the 120,000 pound honeymoon story is that it's not at all clear when they'll be able to go on a honeymoon.
According to my understanding: Meghan will be getting married on a fiance visa. It's a multiple entry visa, but is only good while you're actually a fiance.
Once you get married, you have to convert it to a 2 year spousal visa before you can exit the country with any hope of re-entry. If she changes her name on her US passport, she'd need to get that done before she applies to switch to the spousal visa.
It may be possible to get same-day processing of the switch, but that's not clear from the Eligibility page on Visa premium service (
https://www.gov.uk/ukvi-premium-service-centres/eligibility)