I find that brining makes the fat more stable(firm) after smoking/cooking. For me, without a brine, I end up with a greasy and fatty texture that is undesirable, unless I re-cook the pork belly(reverse sear, fry, bake, broil, etc) after smoking.
You can find good several brine recipes on this site using the search bar.
For just smoking and sauce, I take the internal temperature up to 190-195 to render the fat to a consistency I prefer. You can add bbq sauce for the last hour or so, if you maintain the 225. The lower temperature won't burn the sugars in the sauce and allow it to thicken and glaze the pork belly.
Over here in the States, I get 10-14 lbs(5-7 kilos) pork bellies then cut them to my desired size, usually 3-4 lb(1.5-2 kilos). Some I brine for several days, some a few hours. A 2 kilo piece can take up to 5-6 hours at 225.