@briannawu R6 II looks like a nice entry point to the R system for sure. But there are rumors of an R5 II, but of course nobody knows dates yet. The existing R5 still beats the R6 II in several areas -- the top display is something I would miss by going from my 5D Mark IV to R6 II.

I agree with @kfcrosby to rent the system you are considering. I have used borrowlenses with success in the past, including when they rented me a 3rd party lens with old firmware that errored out my 5D Mark IV body; they made it right and I was able to get by on the trip with that issue. I ended up buying the same lens, later, with updated firmware. So I would use them again.

I borrowed a friend's Sony for a week and long story short I complained about accessing features via menus.

On EF/RF adapters, see Brian Carey's experience with an apparently-unhappy R5 and apparently-unhappy adaptor, https://petapixel.com/2023/02/26/my-strange-ongoing-troubles-with-the-canon-r5. Obviously that is not everyone's experience with adapters, though.