In my experimentation, around 2 or 3 teaspoons per 8 oz seems to be a good, not-too-sweet mixture. Scaled up to 5 gallons, that would be 3/4 to 1 cup of splenda per 5 gallons, if my math is not faulty.
I have only tried small amounts at a time, but I am about to put in another 3 gallon batch, plus a smaller 1 gallon batch. I may back sweeten the 1 gallon batch and see how that goes. Whatever you do, know that adding sucralose to carbonated beverages creates a reaction similar to the Mentos trick. Add in small amounts, and be ready to lose a lot of CO2 from suspension.
After back sweetening, If you are force carbonating, you would just keg it, hook up your CO2 at the desired pressure, and wait. If you are bottle carbonating, you would need to add the right amount of dextrose (or other fermentable sugar) and wait 2 weeks or so.
Not sure if sucralose has a negative effect on viable yeast, as I have never bottle carbonated after adding sucralose. It shouldn't, as it is supposed to be chemically inert, but who knows?
Let us know how it turns out, and what you decide to do.