Creating Proxies / Sequences for RAW Arri 2048x1536

Hello! Greenhorn AE here on a documentary that was shot in both 4k and 2k (predominantly 2k as they realized mid-shoot it was a better workflow).

I'm desperate to understand creating proxies better, and to know what the best proxy resolution for my footage should be? The footage was shot on an ARRI in 2048x1536, 24FPS with a 2:1 Aspect Ratio The settings I have right now are as follows:

My editor wanted to edit in a 2K workflow, so I decided to just create the proxies at the same resolution as the RAW, but gut the file so it would be less cumbersome. I'm also in the predicament of making the 4K proxies into editable 2K proxies, but I'm told that some serious letter boxing will occur when downscaling the footage. 

My biggest issues are as follows:

1. If I create a sequence sourced on the proxies, will that create issues down the line if the sequence needs to change for delivery? (I.E to the colorist, graphics designer, finishing house, etc.)

2. If I were to have to create a new sequence mid post production process, would we be able to just drop in the current proxies and work with them in whatever sequence we choose? 

3. What is the best resolution / aspect ratio to output the proxies for 2K to begin with?

4. What is the best resolution / aspect ratio to output the proxies for the 4K to work with the 2K?

Thanks to anyone who helps me with this in advance, I know the questions may be a bit confusing, but I never got the opportunity to learn about these settings and ratios in the school I went to. Asking for a friend!

Best,

Brianna