Bottling with Malto dextrin, Lactose & Priming Sugar

I'm getting ready to bottle my 5-gallon batch of Coffee Oatmeal Stout. I'd like to add malto dextrin to increase body and mouthfeel, but also add lactose for a little residual sweetness. What do you guys think? Can I even add lactose at bottling time, or should I have done it during the boil. Finally, how much priming sugar should I use. I checked out some calculators but I don't know exactly what they mean by desired level of carbonation. I know I'd like a low level of carbonation, but don't know how to translate this into a number. Will the amount of malto dextrin and/or lactose I use affect the amount of priming sugar?

1/2 cup priming sugar would give low to moderate carbonation (thats subjective and opinion however)

How much lactose you use has no effect on the priming sugar.

In my opinion, forget the maltodextrin. Its fermentable and should be added earlier or you'll get bottle bombs. Besides ,the lactose will give body and a velvety mouthfeel. I've seen cream stout recipes that used 4 oz. (1/4 pound) and milkstouts that used a full pound of lactose. I just bottled my milkstout and used a full pound beause I like it sweet. You might want to use 8 oz. or less if you're just looking for some residual sweetness. Just add at to your bottling bucket with the priming sugar and make sure it gets mixed well without stirring too hard/vigorously.

Malto-dextrine isn't fermentable, so you can use it if you want. It provides mouthfeel and body (making it "thicker") and some slight sweetness. Lactose will just provide sweetness. You can add them all at the same time if you want, at bottling.

so if i add at bottling it should be fine then no bombs?

I would use either this site: http://hbd.org/cgi-bin/recipator/brew/widgets/bp.html or brewing software to help figure out how much sugar to prime with.

Oatmeal stouts are listed (in Beer Smith) as having 1.9-2.5 CO2 volumes... So depending on the temperature the brew fermented at (which will determine how much residual CO2 it has) will determine how much sugar you'll need to prime with. When brewing a style for the first time, I would aim for the middle CO2 volume... So, about 2.2 would work...

Using the site linked above, assuming the brew fermented at 65F, you would use 3.47oz of priming sugar (call it 3.5) if using corn sugar. Slightly less if you used cane sugar (aka turbinado or dememera sugar) at 3.3oz (call it 3.25-3.375oz)... I would ALWAYS measure the priming sugar by weight NOT by volume... Volume is a piss-poor method of measuring priming sugar. With all the effort you put into your brew, doesn't it deserve being primed with some care? If you don't care about how it is in the glass (carbonation plays a big part in how the brew tastes in the glass) then prime as you like... Personally, I'll continue to weigh my priming sugar and know that I'm hitting my target.