Confidence is key. Though whether faked or not, you must portray the role of a 'performer' who is giving the listener what they want. Yes, setting up your rehearsal studio in a way that mimics how you will be on stage is IMO very important. Also setting up monitors in the room so it sounds similar to what your live performance will be. Nothing worse than playing a gig and the guitar player is on the opposite side of the bass player. Visual cues are very important. We find confidence in knowing where each member is at without thinking about it.
Agreed that the band should have some cohesive apparel and attitude. If one guy is in cutoff shorts swinging his hair like a 80's glam metal guy and the bass player is sitting on a stool in spandex, well...lol
Personal story about me that may be helpful: When I was 19 or so I joined an established band that was doing really well. I was completely comfortable in my playing (why I was stolen from another band) but I was always self conscious and nervous before gigs for years. After 4 years of regularly playing for 1000 to 2000 seat venues, I still was self conscious. Near the end of that bands time my largest gig was in front of 11,000 people. I was still knocking knees. Had to have one shot of Jaeger and one beer before every gig. No more, no less. My wife 24 years later laughs at me when I say this because I was able to portray that I was a rock star. I was scared as shitto be honest...
Once show started though, it would all just come together. Almost as if another part of my personality took over. Many times I would not have memory of the actual show the next day. Alice Cooper has stated he would do similar, though he 'became' the performer and lost himself. I was just a kid faking being a rock star when on stage. It did work though.
After I matured in life, the band did a couple of reunion shows 5 years ago after our singer from that band was murdered. The first was a memorial kind of thing with other singers/friends filling in. The second was the original band members singing as a tribute for our lost brother. 20 years later, my confidence was way beyond what I had as a kid. I wasn't scared at all.
Stage presence takes time and experience to get down. Work with it and see what works for you and your band-mates. Likely most important is to have fun on stage. The audience will see that and you will feed from their reaction to it. Nobody feels a performance from a guitar player who looks at his fret board and ignores the guy in front who is drunk and yelling, or the one girl who is dancing (usually the drummers psycho girlfriend) like a acid induced hippy from the 60's. Embrace them and make it part of your personality as a band.
Best!