If I am understanding this correctly, sort of yes. Keep in mind most home wireless routers are in essence three things; router, switch, wireless access point. As far as I know you should be able to set this up as long as you keep the 2.4Ghz Access Points six channels apart.
Now, you cannot have the DGL 4500 running a 5GHz signal and a 2Ghz signal separate from each other, it is only one or the other. You should be able to run the two 2.4Ghz routers if you obey the channel rule, ie run the 4500 on N on channel 1 and then the 4300 on channel 6 providing a G signal do whatever other devices you want. I may try this myself as I am lazy and want my PSP to get on the internet but prefer to run WPA2, which it does not support.
I wouldn't worry too much about using the 5Ghz band, the range on this router regardless is fairly good. I have a large house and it handles coverage pretty well even being in a non central location. I have played around with a Hawking repeater but it is not quite a true repeater. If my house were wired for cat5 I would just run the cables down to an access point.