Might also need 1800/CP support for this. I'm not sure the keys cover for that.
Looks like it does for R1 and R2, and you can use the R3 ISO 1u for the 1u numpad+, but if you use ISO you can't use it there. Might be worth considering a spare R3 1u in with the numpad to cover that like, 1% use case.
Also came here to say numpad in base plx
For something like this those keys in the split off kit are gonna cost probs over twice as much with the per-kit costs, vs the like ≤$15 for having it in base and the potential utility.