first ribs

No need to soak the wood chunks - That is a gasser requirement and all it does is steam off first.

250 dome.

Don't worry about a plateau with ribs. Use the 3-1-1 method. Three hours in the smoke, one hour in foil and UP TO one hour back in the smoke. Ribs are done when you an pick them up with tongs and the bend 90 degs. or you stick them with a toothpick and the tooth pick come sout without resistance.

When you are doing a low and slow make sure the smoke is invisible or a very light blue and then temp stable before putting the meet in. You don't need a lot of wood chunks to achieve the smoke flavor. One or two 3" diameter chunks is enough.

My experience is that untrimmed spares take about an hour longer than St. Louis-style trim. Also, the beginning thickness and weight has some bearing. The spares I've found in my area run from 4 3/4 pounds per slab, up to 6 1/4. Smaller is faster, and usually easier to get tender. Laying the slab flat, as opposed to standing in a rack has given me slightly more tender ribs.

I aim for a dome of 250. Because creosote condenses at 250 in the presence of wood smoke and moisture, I don't soak my wood. (In metal cookers, soaking was necessary to keep the wood from bursting into flame.)A handful of chips on top in the center will do for ribs. Personally, I've never minded strong smoke flavor. However, if you find it objectionable, the lump by itself will give you just a hint of smoke.

As already mentioned, the "3-1-1" method pretty much guarantees good results. I used it exclusively for about a year. However, the best results I've had have been from long indirect cooks lasting about 6 hours from the time the meat went on.