OK now I see you have the reg Big Easy..
As for the legs you can brine them and it helps a lot, or you can just rub and place them in. Now, as for rubs make sure the rub you use if you are using a rub has very low sugar content cause if it's high in sugar then you will end up with a burnt hunk of meat and that ain't good
To prep the legs wash them well then dry them off or leave them in the fridge after cleaning uncovered for a few hrs. This will help you get crispy skin , even if you brine them pat them dry and get the skin dry as you can. Rub a little oil on then then season before cooking.
As for racks, you should have gotten a set of half racks so place those half way in the basket then place the legs on the half racks.
Turn the unit on after you placed the legs in, no need to warm up a Big Easy that's gas fired. Should be done in 40 to 60 mins depending on weather, temp of meat going in at the time.
There are racks made for this unit as you know and they work well, but if you do a little shopping you can find racks that will work. I'll see if I can find the thread where 10 in round racks can be bought for $1.00 to $2.00 a piece. I'll post as soon as I can
As for the shoulder, it's precooked so all you will do is warm it up , you can do that in your oven..
Now if you want to try a Boston Butt thats not precooked let me know, I have a way to do those.......
Tommy
Best of luck, and season that thing real good with oil not Pam spray