In general, I think most folks find trying to operate conventional and command locos on the same track simultaneously is more effort than it is worth. Can be done, but not always intuitive and simple.
Unless the layout is fairly large, it's hard to keep the conventional and command locos far enough apart to avoid collisions for one thing.
Suggest first using one loop or two for conventional and the remaining loop(s) for command and seeing how much effort is involved vs. fun.
Also depends on the locos. Conventional locos only respond to the voltage level on the track they are running on. Command locos (if the command signal is present), whether DCS or TMCC/Legacy will only respond only to signals from the command system in use, regardless of voltage setting.
One potential complication is that if you try to operate a command loco (either PS2/PS3/DCS or TMCC/Legacy) in conventional mode on a layout that has the command signal present, it may not respond to the conventional voltage control, depending on the strength of the command signal at that track location.
All in all, isolating command and conventional locos physically (using blocks, or separate loops) from each other may prove more pleasant.
Another approach is simply using only conventional or command on the layout at any given time, which is probably the simplest approach.
