On electric lap steel with a band my go-to tuning is E7.
From low to high, B D E G# B E.
That low B is the same note as 2nd fret A string in standard tuning, “high bass” tuning some say. .

You don’t really need the low tunings onstage with a bass player.
Solo acoustic, the big low string is nice and I’m happy anywhere between standard low E all the way down to A.
D seems popular these days ; )

D A D G A D, or D A D F# A D

String gauge is whatever works for you, but it’s normally quite a bit heavier than popular slinky electric strings.
Dobro is usually .016 on top for D or E, that’s my usual gauge onstage too.

Depends on the guitar and tuning of course, I use a .028w for a 3rd string on one guitar, .024p for a 4th string on another.

You really have to experiment to find what you like best, but no harm in looking up lap steel string sets and using whatever strikes your fancy to start.

Same deal for the bar itself, you don’t know till you try.
I started out with the dobro standard Stevens bar, eventually morphed into a bullet bar player.

I’ll bet the bar choice followed my tuning preference; the Stevens bar worked great for open E, by the time I’d committed to E7 the bullet made more sense for the slants.

Don’t overthink it!
Relax, play, enjoy, it’ll find you.

Hey Steve, lap steel tone question for ya! I’ve heard you employ a very resonant ‘sitar like’ tone quite often with your Supro Airliner. I remember asking you about it at a show in Denver circa 2103 and you attributed it to a univibe pedal you were using. Does that sound right? It also sounds to me like the tone is usually used in tandem when playing octaves on the steel. Wondering how you achieve that exactly. A wonderful sound. Thanks! – Derek