I'm sure someone has thought of this already but thought I would share it. This is how I created a numeric keypad on my Macbook Pro. I'm not sure if there are better modification keys for other keyboards but I use the fn key but other modification key(s) would work as long as they don't conflict with other shortcuts. If a touchbar is available then other modifiers may work better so that the touchbar can be combined with keyboard keys. I will experiment with that to see what I prefer but the principals are the same.
fn-m = 0
fn-. = .
fn-j = 1
fn-k = 2
fn-l = 3
fn-u = 4
fn-i = 5
fn-o = 6
fn-7 = 7
fn-8 = 8
fn-9 = 9
fn-0 = *
fn-= = +
fn-[Enter/Return] = "="
fn-/ = /
Some of the keys would not need modifying, such as 7,8 & 9 but I thought it would be easier to set them also so I could just keep the fn key down at all times while using the numeric keypad.
You can always add more keys that you regularly use during number entry such as % or ^ or engineering formulas, etc. but the more keys you use up, the greater the chance of conflicting shortcuts