Add commerce to existing D7 site for player registration

hi everyone! i have just been tasked to add commerce capabilities to an existing D7 site. i need to add the capability for parents to pay online for their children's little league registrations. has anyone done anything similar and does anyone have any recommendations.

basically the requirements include:

• i need the parents to be able to register on to many children (i can limit the number to 5 or 6 since no one has that many if it makes it easier)
• the player registration costs drop $20 for each child (i.e. 1st child $140, 2nd $120, 3rd $100 and so forth)
• choose a candy buyout ($35) or a candy fee ($50)
• choose a volunteer buyout ($150) or a refundable volunteer deposit ($75) - the actual refund can be done in paypal or checks from the league to the parent outside of the system

for the player registration it may be easier to have different products associated with the number of children (i.e. 1 child = $140, 2 children = $260, 3 children = $360), but i still need to capture each child's player information (name, grade, school, age, uniform size, etc)

thanks for any recommendations on how to integrate commerce into the existing D7 site.

frank