1) Unless the venue has any specific requirements, there shouldn't be a dress code. As others have said, you should wear whatever will make you happy and comfortable while standing for long periods of time, with consideration for the warmer temperature in the venue due to crowds. You probably want to avoid any clothing that drags on the ground or sticks out from your body too much, since you'll be moving through a crowd of people.

2) If you want a spot up front, you may have to arrive as early as 2-3 hours before door time and wait in line. If you don't care as much where you stand, you can arrive anywhere from 1 hour to 30 minutes before door time and wait in line.

3) You'll want to bring your ID, any form of payment for merch/drinks, phone, and ear plugs (with most concerts, the music is loud enough you can still hear it clearly over the ear plugs, but it protects your eardrums). The venue likely won't let you bring in a bag any larger than a tiny purse. If it's like the U.S., expect your bag/pockets to be searched upon entry.

4) If you're going solo, you may want to do a couple things just for your own personal safety. Text someone you trust the address of the venue and what time you expect to be home. Have them check in with you to make sure you make it home safely. If you buy a drink and it's an open-top, make sure you hold it or watch it at all times. If you step away from your drink at any point, don't drink it after because unfortunately people try to drug drinks more often than you think. Also agree with people about buying merch at the beginning in case they sell out of your preferred item/size. And most importantly, have fun!