Brilliant, don't know why I've not considered it myself! Wonderful insight, I am jelly tbh.
And it's truth! Among the numerous other lacking keyboard operations, this is a noteworthy over/short sightedness. It's a softball ask, but beneath the technical skills of such capable coders. As is using the enter key for confirmation of most any action, etc., so on, ad nauseam, ad infinitum. My only wish is they move with haste to address the ground texture bug, as it mangles flat ground with errant cliff textures.

I don't know but it depends if they used the character code for the numbers or if they used the character in code. You can test it, turn your numlock on and press a number and see if you switch weapons.
You can't currently rebind the hotbar keys, they're hard coded. If you really need to you'll have to use some keyboard remapping software for when you play the game. Check with your keyboard/mouse software to see if it has the ability you're looking for.