Time Capsule with existing router Q's

Question

I've been looking through a bunch of earlier posts here and I just want to make sure I understand my options correctly for my 3rd Gen TC before I start fiddling with settings... I need to change my setup I've used successfully for years because I just moved. Previous setup had internet via Ethernet and I kept my TC up in the attic connected to my iMac via its own network.
Current setup necessitates cable modem/router providing internet to my iMac wirelessly. I'd prefer to still keep the TC in the attic rather than connect it to the router via Ethernet -- so if I've understood everything correctly my only way to do this is to accept that my backups will run at half-speed and use the hidden option-click method of selecting "Join A Wireless Network"? I also understand that I will not be able to connect any other devices to the TC in this setup -- I won't need to, as everything else I need goes through the router.
Since I'm somewhat of a networking newbie can someone please run me through any and all steps needed to accomplish that wireless TC in the attic configuration?
And, can you also please just confirm that it is only the *TC backups* that will have their speed affected by this set-up, and not anything else connected to my router (like Apple TV) and/or internet speed?
Lastly, if I try this setup and ultimately determine the backups are just too painfully slow, am I correct in my understanding that the only other option I have is to plug the TC directly into my router via Ethernet and turn wireless off on the TC? Is there any other setting(s) I need to adjust in order to implement that hard-wired configuration?
Many thanks in advance.

Answer 1

1) TC Firmware to 7.6.4 (I am currently 7.5.1)
2) Airport Utility to 5.6.1 (I am currently 5.5.3)
Let me know if I should do either or both of those?...
Your Gen3 TC is perfectly happy with 7.5.1
I don't think 5.5.3 is any different to 5.6.1, although if you wanted to upgrade that, I would not think it would matter.. unlike upgrading firmware which can do terrible things.
The widget tells you want TM is doing.. you cannot know otherwise.
Here is my current one.
Starting automatic backup
Attempting to mount network destination URL: afp://Ray%20H;AUTH=SRP@TCGen4._afpovertcp._tcp.local/Data
Mounted network destination at mount point: /Volumes/Data using URL: afp://Ray%20H;AUTH=SRP@TCGen4._afpovertcp._tcp.local/Data
Disk image /Volumes/Data/Miniray.sparsebundle mounted at: /Volumes/Time Machine Backups
Backing up to: /Volumes/Time Machine Backups/Backups.backupdb
Using file event preflight for macos
Will copy (2.7 MB) from macos
Found 43 files (2.7 MB) needing backup
1.21 GB required (including padding), 1.42 TB available
Copied 1384 files (125.7 MB) from volume macos.
Using file event preflight for macos
Will copy (73 KB) from macos
Found 15 files (73 KB) needing backup
1.2 GB required (including padding), 1.42 TB available
Copied 1016 files (1.2 MB) from volume macos.
Created new backup: 2014-04-22-062139
Starting post-backup thinning
No post-back up thinning needed: no expired backups exist
Backup completed successfully.
Ejected Time Machine disk image: /Volumes/Data/Miniray.sparsebundle
Ejected Time Machine network volume.
When things go wrong you will see error messages.
Let me get the whole network straight.
You now have a new cable modem router installed.
You have wireless connection from said modem router to the iMac.
The TC is plugged into the cable modem by ethernet and bridged.
You are using Snow Leopard on the computer?? With v5.5.3 utility.
There is one change I would like you to make if the above is correct.
I want you to turn on wireless in the TC.. create a wireless network.
Lets keep everything simple.. call the wireless TC24ghz and setup a different name for 5ghz called TC5ghz.
Set it with wpa2 personal security. A pure alphanumeric password of 8-20 characters.
Then change the iMac to connect to the TC wireless, pick the best one, ie what is the fastest. 5ghz is always better speed if you can get reasonable signal. hold down the option key when you click the airport fan so you can see the details.
If the transmit rate is 150 or more stick with 5ghz.. otherwise select 2.4ghz signal.
Here is the screenshots for setting up wireless.
Click on the wireless network options.
Sorry the names are mixed up from old screenshots.. but that should help you.
Connecting directly to the TC seems to help the computer.. and Time Machine, locate the disk and especially if 5ghz gives you good speed then the backup will work much better than via the main cable modem.