This will be my seventeenth time, but I still look forward to it every year. This time I'm going up the week before as the riding is easier. By Tuesday or so some of the roads can get to be gridlock going into town.
When you do Iron Mt. Road it will end at the highway between Custer and Hermosa, take a left toward Hermosa. That will lead just out of the Hills to Highway 79, take another left, go a half mile or so and take another left onto Highway 40. That leads back into the Hills to Keystone. If you like high speed sweepers it's a great road with very little traffic.
For the person staying in Hill City, a nice morning ride is the road to Deerfield (what little there is of Deerfield). It starts next to the Continental Cafe at the north end of Main Street and also has mostly sweeping turns, may want to watch it a little going down the last big hill (you'll know it when you get there) as a couple of the turns tighten up. I left a couple hundred feet of floorboard behind last year on that one.
Expect a variety of weather. In the years I've been going it has hailed enough to bring the snow plows out in Custer, washed bikes down the street in Deadwood, had frost in the morning (Hill City), been 109 in Rapid and Sturgis, rained for six straight days, been in the nineties during the day and forties at night, and blown up some horrific storms. The storms usually build in the afternoon and move out onto the prairie, so if you come from the east arriving early helps.
You don't need to bring that much with you. Being it's your first time you'll probably buy a bunch of clothes anyway, and everything is available. A set of leathers or other warm clothes is a must if you will ride before ten or after six, as is rain gear.
Do plan some time in Sturgis. I don't get a lot out of rally central anymore, but it is impressive. There is usually parking in the residential areas surrounding downtown if you don't find a spot on Main. Don't park against a yellow curb - they will tow you regardless.
There is a message board on Sturgis.com that has an FAQ board that will answer about anything you'd like to know.