Your picture looks nice but the link is to a thumbnail so it's hard to appreciate it fully. ;)
1: Is there any particular reason you are using the wifi APs for DHCP? In my opinion it would be much better to use pfSense for DHCP on each interface. Doing that makes it much easier to keep track of the leases or to hand out static addresses for filtering purposes. All your admin can be done in the one place rather than having to log in to each AP to change things.
2: Normally you would not bridge them. pfSense will route traffic between them if you have firewall rules in place to allow that so that you can access, say, the AP in zone 2 from a computer in zone 1. The only reason you would bridge the interfaces would be in you had software that needed to see machines in the same subnet. Many media player programs will only look for servers in the same subnet for example.
By default all traffic from the additional interfaces will be blocked so you will need to add firewall rules to allow traffic that you want. Only the LAN interface has a default allow rule.
3: You can add a rule to allow traffic from Zone 2 to the printer but no other address. Better, you can restrict that rule to allow access only from specific clients in zone 2 if you have all static dhcp leases.
4: Squid with Squidguard is a lot more mature (in pfSense at least) but Dansguardian has more/better filtering options.
5: You could use VLANs to get more interfaces in pfSense without having to add further NICs however I don't believe you will need to. Do your switches support VLANs? Do your APs?
Steve