For me, even a 16" is too small for any real productivity tasks. When working, I often need many windows with excel workbooks, powerpoint presentations, and other information displayed at once.
Other times (like now) I'm perfectly happy with the laptop display, as I sit on my couch drinking coffee and reading MacRumors, checking email, etc. I'm also hooked on portability, I can use this thing all over the house.
I have tried many combinations including an iMac and an iPad, and an iMac and a MacBook. I finally settled on a single, large screen MacBook with an external display. I simply go to my desk when I need to do real work.
I opted for a 32" 4K Dell monitor. I'd prefer the Apple version, but for what I do it's overkill. I use one single USB-C capable of charging at 90W, and I use the monitor as a hub for my Logitech receiver, webcam, and audio. Perfect!
Anyway not sure if that's helpful for you in your situation. Every different combination I tried had some kind of compromise. Maybe someday I'll have an M series 16" MacBook with a pro Apple display, which would be perfect.
My monitor, if interested:
https://smile.amazon.com/gp/product/B07HDBD9CM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1. Good luck with your new Mac!
Tim