Coping with Developer's expansion

As a new member of the Advisory Board for our HOA, I have been given the tasks of determining size and type of future amenities and traffic and safety considerations for our growing community. We started off with a developer who had 850 single family units on the plan. The new group has increased that to about 1500 mixed units.
The current amenities constructed for the original plan: 1 pool; 2 tennis courts; club house (99 persons max.) some walking trails and small water retention areas for fishing appear to be insuficient for the future. We did a survey with the current residents and got some diverse feedback. (At least 2 more tennis courts for league ability, a new club house for 300 persons; exercise rooms; expanded and heated pool; etc. What would be the best method to determine our future needs and who should pay for these expansions (HOA or Dev.)?

As for Traffic & Safety we have a 30mph posted speed limit. Many stop signs etc. and still many speeders (both residents and contractors). We have arranged with our local police dept. to enforce the limits on the main roads but they cannot be everywhere all the time. How do we make drivers adhere to the rules? Can we install "no thru traffic" signs to cut out the "short cutters"?
Should we consider a "local HOA enforcement group" to issue HOA tickets?
Any info would be appreciated.
DonT

Roger
Thanks for your reply. In answer to your questions, the developer, not the HOA has decided on the size increase. The HOA is now trying to determine the size and shape of any increase in amenities which will be required and paid for or shared by the developer. We would like to find out what any other HOA of that proposed size has in the form of amenities.

Our streets are still private but permission to patrol has been contracted to our local town. Our next step will probably to erect "no through traffic" signs.
DonT