there are other layouts with numpad, like 1800, or nym96/melody96.

also, you always have the option of a separate numpad. with it, you will have more options than southpaw or full.

you can use any kit, as long as the pcb supports mx-style switches.
boards at that range usually don't offer good typing experience, unless you put efforts to make them better.
maybe you should start by stating your budget

of the three, tecware phantom elite should be better for you, because you can swap its stock switches with other 3-pin switches later.

if you are interested in testing different mx style switches later on with one board, then don't get tecware phantom L. they use low-profile key switches, with outemu sockets, which narrow down limited options even more.

you can swap the switches out, and replace them with non-clicky ones, like 3-pin gateron. it's a simple process.

imo 'preference' is the much better word for 'better' in terms of switch choices.

tbh, it's really up to you to decide which one you're after. i suggested tecware phantom elite because i think you might try out other switch types later on, and you can do it right away, by getting some and put them on.

it depends on conditions. afaik rk71 is a soldered board. if you are proficient in soldering/desoldering, it's good to go for switch swapping. for key cap swapping, rk71 has key caps that are not fully compatible with standard layouts (check out the keys on the right side of the board), but you might be able to use different profiles, such as xda/dsa. (i guess)

imo for starter, it's better to use hot-swap boards (with kailh/gateron switch sockets, 5-pin switch support, south facing switch orientation), so that it's convenient for you to swap switches on-the-fly. also, use standard layouts if possible, so that there is no funny limits to use different profiles.