Regarding your E113 error, the message points to "top.loader_scheduler.loader_scheduler" - so search in that code for creation of primitive channels.
Regarding your second issue, it's easiest to have all processes running all the time, and then delay the start of each processor model's processing I think - if I've understood what you want to do. I.e. have your MIPS models in some kind of idle loop until you want them to start.
There isn't an easy way to restart simulation. You can however call sc_start multiple times, so perhaps you could do
sc_start(1, SC_MS);
// start processor 2
sc_start(1, SC_MS);
//start processor 3
etc.
As I say, your model sounds complicated to an outside!
regards
Alan