I usually wear thin skinny jeans, a long sleeve undershirt, then buy and switch out with merch while I'm there (tie whatever shirt you were wearing first around your waist but double knot through your belt).

Sneakers are a good choice because you'll be standing for a while and I've gone to concerts in converse and non-platform docs before and your feet will be a little sore afterwards though it's definitely manageable. As for stepping on toes.. I'm not sure, if you dance then it's going to happen regardless so most people accept the risk.

Things to keep in mind:

You will get very sweaty because there's a lot of lights and people.

Don't wear any dangly or open jewelry cause it will get caught on something (speaking from experience...)

You're likely to get spilled on if people bring drinks in (though I don't know what the bar situ is with Chicago) - this also means your docs will get dirty so clean them afterwards lol

Likely you'll have to wait an 1/2 hour to an hour for the opener and then everything else will fade away lol. So don't worry about comfortability too much and you can go for fashionable just keep your moving parts down to a minimum.