Well, a toilet requires either a 3 or 4" drain pipe. If you use a 4", you can pour the concrete right up to the pipe, since you can use an internal fitting flange. If you use 3", you should put the flange on the outside (an option with 4"). Since it needs to fit around the pipe, you need to put a removeable sleeve around the pipe so that you can get the flange on later. The majority of toilets in the USA are 12" rough in. That means that the center of the drain from the FINISHED wall is 12". Better to be a little bigger than smaller, since when you go with the normally available alternatives, you end up with 10, or 14". You need a vent line for each device (sink and toilet). The drain for the sink is usually in the wall behind the sink. A sink drain line is often 1.5", but there is often a minimum size (2"?) if it is going to be under concrete. Make sure to use the right fittings so that things can be snaked, if it ever becomes necessary, and maintain the 1/4" per foot drop for the drains. The vent lines can be combined above the flood plane of the sink (nominally 42"), then goes up through the roof. Don't try to get the toilet flange at the 'right' height, just leave it long and cut it off when you do the finished floor. The flange is best installed on top of the finished floor.