Medicated starter contains a coccidiastat, NOT an anti-biotic. Coccidiastats only prevent the natural exposure to coccidia from overwhelming the gut and killing the chicks. Coccidiastats only affect the coccidia - by inhibiting their vitamin uptake.
If doing it without I'd suggest going to either raising chicks or feeding and watering the flock and asking about things you can do to prevent coccidia from killing your chicks over the next three months.