I've been considering adventuring into ergo-mech keyboards, but my hesitation is that I use the number pad a lot in my work. I also make use of the special character mapping codes, like "alt + 0176" for the degree symbol, that only seem to work with the number pad.
Given your write-up, it looks like I would need to map a layer to match my needs in this area. Would you agree?
If you're typing in alt codes, it sounds like you would definitely benefit from a keyboard where you could program those to keys, whether or not it was ergonomic. I wrote about customizing qmk with programming to meet my needs, but I'm a programmer-- there are also GUI configuration tools that might suit you better. Most (all?) qmk keyboards can be configured with a GUI tool called VIA.