It's really good that you're looking at doing weight training. It's healthy for a variety of reasons.
You should in any event, be able to add a few pounds of muscle and lose
the weight you want, over the next year. It sounds like you're thinking
about more than a few though....
The max amount of pure muscle that can be put on by an untrained individual
is about 2 pounds per month for men (about half that for women). As you become further trained and closer to your muscluar genetic potential,
it the amount of muscle you can put on decreases. I don't think this
is your immediate concern though
. Nor mine.
In any event, the problem is that you also want to lose weight, 20
pounds of fat or so. When you are trying to work those things at the same
time, it is harder. You are telling your body to shrink and grow other day perhaps. It's a mixed message to some degree.
Unfortunately the body doesn't convert fat into muscle, though it can
use fat to recovery energy. You need to eat more protein and calories
to gain mass.
As well, when you gain back weight, it tends to go back on at your current bf%. If you added a pound of weight, about 20% (if you were around 20% bf) would get put back on as fat, creating more fat for you to lose. (Estimating another 20% would go to glycogen stores, 30% water balance and 30% perhaps towards protein balance requirements). It's a 1 step back and two steps forward 1scenario.
What I'm saying is to have realistic expectations. Consider making fat loss the priority, and have a goal of being steady with the weights. Focus on strength gains rather than muscle size. As you lose fat you will look more muscular in any event
After you have taken off the 20 pounds of fat, then consider getting
serious about adding more muscle.