Best leave the brown sugar out of it. 1/2 CUP won't make the beer drier or lighter-bodied by any perceptible amount, but it won't make it any sweeter, either.
Avoid flaked grains unless you're mashing. You'll get nothing but glop in your kettle, and nothing but haze in your beer.
Dextrine malt (CaraPils) can be added to enhance body. I don't think you need it, but others might disagree. 8 ounces ought to be sufficient.
As will lactose (brewer's milk sugar). Again, 8 ounces ought to do it. Don't use lactose and CaraPils together!
Neither will add much sweetness, but will enhance body considerably.
Really, I'd use neither. I'd add four to six ounces of a darker crystal - like 80-90L - to the steep. A different sort of sweet, but still sweet, along with the body and mouthfeel enhancements crystal malt can provide.
If you're adding spices, avoid flavor/aroma hops. They will compete too much with the spices, muddling everything. Think of hops as a spice and try to imagine the cinnamon blend with hops in. Usually, it doesn't work very well. Try it - boil your proposed blend of five-minute additions in some water, then taste the tea. It won't be very nice.
There are two other methods of spicing your beer.
You can just brew a brown ale (your basic recipe). When you're ready to bottle, you can boil up a tea of your spices in a pint of water for five minutes or so. Then add the strained tea incrementally to your primed beer before packaging. Taste after each addition. When you go slightly too far, slightly too spicy, stop. The excess flavor will attenuate in the bottle, leaving you with the perfect amount.
The other method is one I use with holiday beers: On the day of a party, I decant a sixer or so into a crock-pot, add a cinnamon stick, a half-dozen whole cloves, and a grating of fresh nutmeg. Let warm for a few hours. Yes, it'll be flat. Yes, it'll be spicy, warm, flavorful and brilliant.