NTU application:

1)NTU definitely opting for olympiad medalist or person who performed well in international arena only.. i don think school or state level affect much.. National level is something like national robotics competition, national physics competition and so on(provided u must achieve not participate only).. but no harm if u fill in watever events/clubs that u think is best for u.. because they will never reject u due to that matters..

FYI, NUS and NTU admission strictly based on meritocracy ONLY.. unless u possess a very very outstanding achievement in co-cu as stated..

if u're choosing engineerin or business courses.. i can assure the chances to get admitted is equal to zero.. but since u're intended to pursue in art stream.. i guess u still stand a chance and no harm to give a try.. good luck..