How many nic single port can i use in pfsense?
How many are accepted? Is it better to use 4port nic or 4 singleport nic?
As many as your slots (PCI or PCIexpress NICs) PLUS as many USB ports as you have (or are prepared to provide through hubs).
If you have VLAN capable switches you can use a single port NIC and have as many VLANs as you want (up to at least a thousand).
If you want more than a couple of interfaces you will probably find that a good quality VLAN capable NIC with VLAN capable switches will cost less than multiple good quality NICs.