Maybe the best piece of advice is to bring your cell phone. You will almost certainly forget something you need.

Remember, when we were kids, we didn't carry any of this jazz, and we did OK, so don't get too stressed out about it. The worst that can happen is you have a nice long walk to think about it.

To solve your tube problems, get some rim grommets. Since your rim is drilled for schrader valves, you can use any tube you can beg, borrow, or steal if the need arises.

Not trying to start an argument with you, guy, but....

Riding the wrong way is dangerous because, being against the law, NO ONE in a car expects to see you there. The increased closure rate you refer to is deadly under the wrong conditions. And, no -- you're not likely to spot a drunk or a text fiend in time to do anything but say, "OH SH**!"

Hits from the rear are less than 3% of all bike/car crashes, IIRC.

I agree with the dry run first. Also be aware of how you feel after you do it. Make small adjustments as necessary (raising/lowering saddle, adjusting tilt, fore/aft position, etc.), but not all at once. Think about what you need to bring to work, and what you can store their as well. If you sweat a lot or don't want to feel scumy have baby wipes available.

A Backpack might be fine at first as well. If you have the money, there is nothing wrong with having a rack. Also learn how to fix a flat, before you need to fix a flat. Learn basic bike maintenance as well. I would hold off on all the accessories until you know you will keep doing it. A rear blinkie like the Superflash, and a front blink or steady light should be enough if you are not commuting at night.

Anyways good luck, and let us know how your dry run goes.