A lot of water comes out of the meat or vegetables, you won't need to add much. If the sauce is too watery boil off the water at the end. BIR sauce usually comes up a lot thicker than some traditional stuff, but with a bit of extra cooking you'll be fine.
If it's bland, look at the recipes/ method you're using. I can recommend some from here if you wish. Some people prefer BIR style to traditional but I like mixing them up, some of my favourite on-the-bone recipes are traditional style.