How to install DWV piping for new toilets added to current system
You'll want to match your 4" house line with 4" to both locations. And yes, if you can toss in an in-line vent halfway along those runs, that would only be beneficial.

And yes again, you'll want to continue the 4" at each location as their own separate vent stacks. Through the roof or higher than all fixtures through the wall. 

Additionally, in order to avoid having to vent other fixtures (if any) separately or by tying them into the location's vent stack, you'll need to keep those other drain inlets (if any) no further than 5' from the vent stack. Otherwise no, the vent stack would be just be for the toilet.