This may differ among schools. My son's profile was a 5 page doc (cover + parents' words + my son's details and some photos (2 pages) + artwork) and he got offers from 4 schools last year. For 叩門, I'd suggest that you write a formal request letter in addition to submitting the profile.
2. 興趣班證書可唔可以縮印?
I don't think copies of certs are useful (and that's why I didn't include any in my son's profile). Just list out the interest classes your child has attended / is attending all on one page.