750GL, PPPoE and a routed subnet

ether1 is a PPPoE link to my ISP, with a routed subnet (x.x.x.176/29). This I can configure successfully: the router connects to the ISP and gets the correct IP (x.x.x.182)

What do you mean by correct IP? mean Public IP?
Are x.x.x.176/29 public or private?

I’d like to reserve ether2 for a secondary WAN link, to be set up later.

Don’t touch it or disable it.

I’d like to use ether3-5 for devices with static IPs on the routed subnet x.x.x.176/29

If These are public IP and you have to route them to your clients.

I think you need to take a TCP /IP tour or hire a consultant.
Or
can explain us more which can help you

It is also useful,
http://forum.mikrotik.com/t/getting-the-most-out-of-this-forum/40983/1