1)Marquee is another club that you can expect to hear trance and house music, unfortunately there's nothing listed on either of the nights you're here, but it's worth noting for future as both Gareth Emery and Dash Berlin play there regularly.
2) I only go to Vegas around WSOP time and have one experience with going on a random wednesday night (which happened to be Surrender) and it was pretty enjoyable, but not 'EDM' based.
3) I don't think people do go to these sorts of things alone USUALLY, but I (and I suspect many posters ITT) would go to something alone if they were really excited about the line up. For the most part, however, I'd suggest it's considered a group activity.
4) Yes that's normal for Vegas, if not more expensive if it's a bigger DJ
5) I've not seen Chris Lake but I'd probably suggest dipping your toes in the water if you can. As much as we love to post amazing songs and sets etc, being in the crowd is a completely different experience and I'd advise you start your dance music journey as soon as possible.
Hope I've been of some help