Get the fs-i6 or fs-i6x. It's a nice entry level rig, it's not the best. They've already pointed out you may outgrow it pretty quick, but i'm still not at that level.
I'm cheap and don't need channel mixing for hydros. You could probably put the hydro esc on an aux channel with a Pot running it, and treat it like hand throttle for setting idle / running speed? Maybe put it on the normal/acrobatic mode switch? I dunno, i built a cable-machine to avoid all that.
https://oscarliang.com/flysky-tx-rx-buyers-guide/
The easy answer for RX is either:
Fs-ia6
Fs-ia6b
Standard connectors, all plug&play.
I'll try to dig deeper, there are also 8 / 10 channel rx that work too, and can send telemetry back to the tx if you add sensors. Or if you're tight on space, there are some that should work with extra soldering.
Helpful non-airplane setup guide
http://runamok.tech/RunAmok/flysky_i6.html