What I'm looking to achieve:
1. Improved wifi coverage. Idea was to name router wifi and password the same as TC and AE and in effect have 3 networks that all devices can connect to without issue. I'd like to know if this is recommended and if so any advice on things to watch out for. I see in an earlier post that an option is to have them all the same even across non-apple kit. If this is possible I was going to move my TC upstairs and swap it into where I have the AEand then put the AE in another room to be able to stream music to a stereo.
You are using roaming network which is the best way to do it.
All of the wireless, including the Huawei can use the same wireless name and security credintals.
The only thing to watch out is channels for 2.4ghz, as they are limited to 3 that do not overlap, 1, 6, 11 (13 in UK and most of Europe). The auto settings in most routers can lead to chaos so it is worth stepping in and controlling the wireless channels manually.
Also take the time with a laptop of whatever breed and do a wireless survey around the house to determine the black spots. Inssider on PC is excellent.. and Apple have built in quite good diagnostics since Mountain Lion.
See http://support.apple.com/kb/HT5606
The only problem with moving the TC is I am unsure where your MacMini lives.. if at all possible you want ethernet to that box or fast AC wireless.. as backup and sharing from that will need the fastest link.
2. Streaming of movies and music. Currently using REMOTE app works well with ATV but my ipad takes an eternity (when it works) to connect to the 'home shared' itunes library. I've read that this can be an issue with large libraries or when it is done over wifi...hence my idea to use the router's wifi to help create better wifi coverage.
Network speeds are often the key.. and yes, wireless is a problem.. double hop wireless between items.. is slow.. meaning any devices that connect to the same router / AP that are both on wireless is going to be slow. You want ethernet as much as possible. Even using EOP can be just as slow as wireless unless your getting good speeds out of it.
I also wonder if using an old 5400 rpm hard drive just doesn't cut it? So I am now considering investing in a NAS for my setup. If Ido this would I connect it to the router or MacMini as I want all the devices on the network to be able to access it. Also I'm probably going for a non-RAiD solution to keep costs down so will I be able to back it up to my TC (was looking at a Lacie d2 as it has time machine backup capability and can do itunes serving).
Network network network.. that is your problem.. and actually it is simpler than that.. it is wireless.. and perhaps the EOP adapter. 5400rpm drive is no problem.. most NAS are fitted with cheaper green drives.. that is not the issue.. ethernet even at gigabit gives you a speed near to the speed of transfer of the slow disks.. the problem is the actual processor in the NAS will have to be fairly high power to give good speeds. (Loads of RAM as well). Your current external drive .. is it connected by USB2.. there is a problem.. but no where near as big as wireless.
itunes serving btw might not be all you think it is.. iTunes still needs a computer in the mix for movies .. none of those cut down iTunes servers does video streaming AFAIK!!
If you do buy a NAS it plugs by gigabit into the fastest router you have.
Backup is not so easy either as Time Machine cannot backup network drives.
Also are there any connectivity issues associated with having some devices physically connected to the router that will need to access data / be controlled from devices attached to other networking devices...eg TC??
Loads of issues.. it is usually better to settle on one system and stick to it.. A NAS is great. But if you want to use iTunes library on the NAS it is not so great. iTunes is much better on an external disk plugged into a Mac by the fastest interface you have.. well thunderbolt is too expensive for us mere mortals for now.. but USB3 is excellent and cheap. FW800 is old standard and best you will get on most older Macs .. but there are plenty of poor FW800 around (WD stand up now please) that are same speed as USB2.
But plugging ethernet into the Mac directly is irrelevant.. it is still network.. and therefore no different to plugging into the router.
Good luck..
BTW.. spend the money and run ethernet.