the mc should start designing a system, using his 'creation quirk' teh system should be up and running before chunnin momoshiki exams or probably it would be better for it to be ready around the time he graduates from the academy.
i think you should show most filler stories that happen during the pre timeskip era coz we dont really know too much about the future rn and he might make a mistake that needs fixing, although dont do too many fillers just a few, thanks.