Well, there are ways to look good without looking at the screen.
1. Have a vocalist who knows the songs you will play. These are entirely up to you, so find 35-40 minutes worth of songs that your vocalist can memorize perfectly and you're fine. Memorizing solos, or at least being able to give some attention to the audience now and then during them, is also really helpful, but it's entirely normal for REAL bands to not pay much attention to the audience. You'll often find bassists looking at their hands intently or closing their eyes and grooving out if they're really comfortable with what they're doing. Guitarists often do the same thing, but have a tendency to pay more attention to other members of the band. Drummers almost always stare off into space while they drum; 4 of the 5 I've played with have done that. So yeah, don't worry about that too much.
2. Coordinating outfits well is a huge deal. If everyone cosplays from the same anime, as a group who works together, or everyone dresses up as storm troopers, or everyone wears otherwise well-coordinated outfits, it will be a huge addition to their score. Pikachu's Rotting Carcass scored perfectly from all three judges in the entertainment category last year IIRC, mainly because Washu, the vocalist, put on a fantastic show. I can't even remember the rest of the band.
3. Get in touch with the audience and judges while you're getting on stage, and between songs. During the song, just play well and leave it to the vocalist to entertain otherwise.
4. Find a balance between difficulty and score. If a couple people need to drop to hard to get those 4-stars up to 5-stars, then do that.
Another thing I want to mention is that bands consisting of 4 people will have priority over incomplete bands, including those where a vocalist sings, or bands that plan on playing songs without a vocalist. If you can complete your band before the con, that would be best. If not, we can help you find folks looking for a band to join, but coordinating beforehand is your best bet, especially for getting a decent vocalist with whom you can practice your setlist.