NAV 2011 and Windows firewall

Im running NAV with agressive settings (maximum protection)

 

1. Do i need Windows firewall?

2. Should i disable it?

3. Is there any conflicts or slowdown?

4.Is it overkill to have both Inturisom prevention and Firewall, knowing i dont visit rally dangerous sites? ( i know they are not the same btw)

5. Does Windows firewall slow down browsing?

 

Thanks and sorry for a bit offtopic.