What interferencers want from a tribute band is one thing, what bookers and agents want is probably entirely different... unfortunately you will depend on these guys to get booked, there's a certain amount you can do yourself but once it comes to bigger and better gigs you're going nowhere without them on your side, and virtually all of them (in my experience at least) prefer tribute bands that look and sound very similar to the originals because that makes it far easier for them to sell you to their buyers. You don't have to be a dead ringer for Bono but without at least an attempt at the look I think it's unlikely that any serious booker will be interested and you'll be lucky to play any shows other than local pubs... As far as sound goes, if your band doesn't sound at least a bit like U2, i.e. the guitarist refuses to use delay, and the drummer's main influence is metal, and it shows, you're in for a struggle. Have a look at the market leaders in the UK and elsewhere, determine what they are doing right and copy it. Seriously. Originality is not a good thing in a self-advertised tribute. Oh, and if you possibly can, I'd lose the keyboard player and learn to work with sequences; your fifth member will raise costs, reduce income, and the more people there are in the band the harder it is to keep everyone happy. Also, learning to play to a click will make your drummer a better drummer and you will all sound better as a result. Making decent sequences is hard and can be expensive but it will probably pay for itself quite quickly... all in my opinion of course, good luck with the project.