Is creating a new network like this the best scenario? Or is it better to extend the existing Optus wireless network? Besides extension for range/reception, does either option have particular benefits over the other?
I would say it is about 50-50.. 6 of one .. half a dozen of the other.
Any scenario you dream up has a set of good points and bad points.
So some factors.
1. I presume you have the TC plugged by ethernet into the Sagem modem.. bridged and creating its own network.. using two different network names keeps the local connection load contained which is good thing.
Wireless is fundamentally poor. It has limits on being only able to handle a single client at a time.. so time slicing between all the clients. plus it is half duplex.. which is simply it can either transmit or receive not both.
In comparison, Ethernet via modern switches.. can have multiple computers talking to each other at once and can both tx and rx, ie full duplex. So using extend wireless is very bad. It means wireless is much slower as each packet is double handled.
Using multiple APs connected back by ethernet to a main router is definitely the right way to go. They can be in roaming or setup with completely different names.. that is almost irrelevant. It is easier though to manage when you do the naming and setup so you specifically allocate load.
For example.. if the TC is doing backups from TM on the computers and you start having streaming issues with the Apple TV, split the load, by naming the 2.4ghz and 5ghz differently in the TC.. and force backups to 5ghz and streaming to 2.4ghz (or visa versa depending on range issues etc.).
2. Network wise different AP should all live happily together in one happy family. The reality is that more equipment leads to more issues. I have been hitting a few issues lately with wireless routers exactly in your setup being unavailable to the network, if a computer happens to be connected to the wrong router.
For example a computer connected to the Sagem, whether by wireless or ethernet, may have issues backing up to the TC. It shouldn't but it does. I am seeing Mavericks in particular giving strife this way.
Someone recently posted a very helpful article on why this is happening.
https://discussions.apple.com/thread/5863043?tstart=0
For most people in a home network you do not want the hassle of running a server. But you can see that sometimes things start getting complicated.
Best principle is hope for the best.. set it up as per what you have done.. if it bombs or is unstable.. work back through the issues.. there are some alternative configurations which are more complicated.. eg running the TC with static IP, that seems to alleviate some of the bugs.
3. What works is best. Whatever the theory.. try a few setups.. what you setup that works well for you is the best even if the theory says no.. that is bad.
eg One post a person used roaming network with all AP's fixed to the same channel, so the idevices would roam properly. This is wrong.. but works.. normal roaming network laptops seem to be able to roam well but idevices do not. Pick what works.
https://discussions.apple.com/thread/5983145?answerId=25138680022#25138680022&ac_cid=tw123456#25138680
