Gaining weight now before HRT sounds like a mistake. I put on 25 pounds of muscle in my last hurrah of dudeliness and I regret it.
When you start HRT, you will start to put on fat deposits in "girly places". You won't now. Also, your metabloism will slow and gaining weight will become, umm, easier. Ever since I started progesterone, all I have to do is look at food and I gain weight.
You probably need to adjust your intake on the fly. You will know if the new fat is going where it should or not. During the holidays I increased my intake. Some of it went where I wanted it to, some didn't. Seems that was too much, and I'm back to losing weight SLOWLY. I don't want it coming off my brand new bewbs!
I hope that was helpful.