Randy, you've gotten great advice already, so I'm just gonna add a bit to that.
It might be fun to start with a chicken or something, just to get the thing working and see how it works. But don't expect the skin to be very good-- I find that smoking a temp at WSM temps makes some great meat, but really rubbery skin. Just the same, it's a good place to start.
Ribs are a nice trial run, too, since they 'only' take 5 or so hours.
+1 on getting it gunked up before it'll cook quite right. I bought mine used, and it was plenty 'seasoned'. But it still took maybe 6 cooks before it started to run nice and steady for me. So be patient. I've heard of people smoking bacon and/or other cuts of cheap meat, just to season the smoker.
When you do take a try at pork shoulder-- and you really should as soon as you have the time-- I think you should start with the ending. Which is to say, you'll be pulling your meat off at 190 or higher, and you should wrap it tightly in foil, wrap that in a towel, and pack the meat into a small cooler to stay warm and rest for at least an hour. The good news is that you can go ahead and leave it in there for at least 4 hours before it gets anywhere close to 140 (a very safe range for pork). So start with the ending, and give yourself plenty of time (this is good advice in general when it comes to WSM cooking and butts in particular). If you're wanting to eat at 5, guestimate your finish time toward 12 or 1, so you have some time to play with. Then you won't be trying to race to the end, or all worried about things. In the case of butts, I start them the night before, since they usually take me between 14 and 19 hours.
And like others have said, GO SLOW. Fill the coal ring up with cold charcoal, but only use about 10 coals to get it started. When it's rising up to within 25 degrees of your target, choke the vents down to slow it down even more (it's easy to bring it up to temp, but it's really hard to bring it back down). If you do make adjustments to the vents or coals or whatever, don't expect to see the results of those changes for about an hour (remember, the WSM is built for SLOW). Once it gets settled in where you like it, I think you'll find that it holds really steady at that temp for hours and hours and hours. Last time I did an overnight smoke (2 butts), I didn't even get out of bed once.
Your smoker is gorgeous-- congrats on your patience and reward. The handle is in incredible condition! And that's an amazing price (I paid 85 for mine, and am still stoked about that deal). I'm really happy for you.