BIG IP 1600 - Trunk configuration - More than 4 ISP Internet providers

That should be relatively straightforward.

Create a single trunk using LACP, add interfaces Eth1.1-1.3 to the trunk. Create your VLANS 100,200,300,400 on the LTM making sure to reference the appropriate tag number in the VLAN. Create your Self IP's on VLANs 100,200,300,400 Create your Floating Self IP's on VLANs 100,200,300,400 (I would suggest locking down your ISP IP's to NO access)

You may also want to create a LAN enabled crossover interface for Network Fail Over that is not one of your ISP VLANs. (Do not do port lockdown on this interface) Add a /30 IP to the crossover between the LTM for Network Fail Over and sync.

I think some people would question being outside of the firewall, I tend to be one of those people, but you are also load balancing ISPs. Just be careful not to permit access from the internet to any self IP on the LTM and you should be ok.