Seems you are headed in the right direction. And, yes, uxpShowModal() aliases to showModal() for now, but I think that is expected to change in the future…
The sp- components are definitely hit or miss in my experience.
As for the production “ready-ness” of UXP, I guess that is up for debate. Adobe seems to think it is production ready. UXP does work well for some projects but has many unimplemented features so I definitely don’t think it is a top area of focus/priority for them.
Cheers!