By default the A+ will assume that you connect the router directly to the internet. So it will be set to Router mode, so will provide it's own Firewall and DHCP.
Using an A+ to "provide extra ports" sound like a bit overkill. For this I suggest you get a switch, the A+ will use more energy than for example a simple Switch.
If you really want to use the A+ for this then configure it in AP(Access point) mode instead. You can also log into the OpenWRT interface and just turn of the DHCP server, then you can use the 4 switch ports just as you would any other switch.
-Edit-
By the way just thought of something.
You said your devices do not get an IP at all?
This is not correct behaviour, by default they should get an IP, however it could be that if your main router is in the same IP range as the Almond+ then they might conflict, try setting it differently from the LCD GUI.