Need advice on best way to set up my network of Apple products (Help!)

I just bought an Apple Time Capsule* and I'm wondering what would be the best way to integrate it with my network and all of the devices I have now. I've never owned a Time Capsule so I'm still learning all of its capabilities (bare with me)

I plan on using the Time Capsule either as an extender (hard wired) or turn off the wireless on the Motorola altogether and use the TC as my wireless router. Whichever way works best in my modest 2 bedrm apt. Streaming is inconsistent in the bedrooms currently.

*I bought the old Time Capsule (2011)

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First a list of my hardware:

I have TWC (100 Mbps/5 Mbps) using their Motorola SURFboard SB6121 DOC SIS 3.0 router

2011 iMac - Running Mavericks

(2007) Macbook Pro - Running Snow Leopard

iPad Mini, 3 - iPhones (4s, 5, & 5s)

Apple TV, Roku 3 & PS3

Notes:

My iMac, PS3 and the Time Capsule will all be hardwired

The Apple TV and Roku are in bedrooms using Wifi

My initial concern is should I use the TC as a extender/Roaming network or shut off the medicre wifi on the Motorola and use the TC as my only wifi router? (It'll be better placed in the center of my apt compared to my Motorola router)

I've read that it does dual band automatically so I'll probably leave that alone.

After that's setup, should I use it as a file sever for my media or continue to use my iMac? I have 10,000 songs and hundreds of digital TV shows/Films that taking up space on my iMac's HDD.

I'm nervous about screwing with iTunes, iPhoto directories so I'll probably just leave that as is. For other media outside of iTunes I'm currently using Plex. Is there a better way to organize my media and stream it to ALL of my devices?

Any help, input or experiences are appreciated. Like I said I'm a noob at using Apple's networking hardware and want to use it to it's fullest.

Thanks!