If you advertise as BBW then you'll attract the right clients. Make sure your photos highlight your curviest bits. Don't fall into the trap of layers and loose clothing to hide your body, the clients you want to see LOVE big women in all our curvy, jiggly glory
When you're new you might want to start with a lower price until you get some reviews, then raise your prices. I started at 100/hour which is low in the south east, then after getting some good reviews I went up to 120. I'm in London today and have gone up to 140 and my phone has rung constantly.
I have an app on my phone called "SMS Signature" and it allows me to save some pre-worded text and then quickly paste it into a message. I have one saved that says "My normal working hours are 8am-8pm Monday to Friday, weekends by prior arrangement. Please call me to arrange a booking" and I send that to anyone who's texted me up til 11pm. Any texts that come in between 11pm to 7am get ignored, usually these are the "u workin?" variety. If I get a sensible text in the night and the guy says he's a shift worker then I'll text back. But most midnight texters are drunk or high IME.
Are you using a separate phone for work? Please make sure you are. You can buy a cheap Android phone from O2 for about ?30 on PAYG.