Basta clearly defines ang requirements ay ok lang.
Validations: research everything about security front end & back end. sql injection, brute force, cross site request forgery!...
Tingin mahihirapan kayo sa SMS, kasi kailangan nyo ng modem at kailangan nyo kumausap sa globe or pldt... Gagastus kayo dito.
If you need consultant PM me. hahahha!.. mura lang : )