First time connection, clueless user

Question

Hello all and thanks for the help.
I just bought an Airport capsule I intend to use for the following:
- To back up 2 computers using Time machine
- To be able to exchange files between computers (or if easier) simply move files from one computer to the other using Time machine back ups - manually
SPECS
1. Computers:
- imac 3.2Ghz Intel Core i5, 16GB
- Brand new MacBook Pro 2.8 Dual Core Intel i5, 16GB
2. OS and software: All of them running 10.9.4, Time Machine 1.3, Airport Utility 6.3.2
3. Internet conection:
- A small, Comcast Netgear wireless router that has several opened Ethernet connections. To it there are two things connected: a Sonos system device and a cable connecting the router to the modem, but again, there are several slots opened
- A medium size, black, vertically  resting DSLModem: Arris TM722 (there is only one Ethernet slot on this, and it is taken by a connection between it and the Comcast receiver)
QUESTIONS
1. How should I make the cable connections for first time set up of the capsule and for later ongoing use
2. This may be an unrelated to this topic, but FYI: the laptop is brand new, so I will need to bring some files and data from the iMac to the laptop, not sure what method will use... but may use a manual method from Time machine if possible.
THANKS
Alberto.

Answer 1

The modem is not dsl, it is a cable modem with telephone ability.. the phone cables might be confusing you but there should be a thick coaxial cable going into the modem which is the cable connector.
Comcast Netgear wireless router
I am not aware of comcast supplying a wireless router.. if it is specifically from comcast you maybe stuck with it.. but i would try to plug the TC directly into the Arris modem.
Power cycle the modem.. this is more complex with your model if the battery is present.
The TC should be in standard router mode and the public IP should then be loaded onto the WAN interface of the TC.
No luck you will need to leave the netgear in place and plug the TC into that with ethernet.. but in this case you will bridge the TC instead of using it as router.
1. How should I make the cable connections for first time set up of the capsule and for later ongoing use
Ethernet is always best. Especially for the first backup.
Your new laptop may not even have an ethernet port. In which case wireless should be fine.. unless you want to buy the thunderbolt to ethernet adapter which is only around $40.
2. This may be an unrelated to this topic, but FYI: the laptop is brand new, so I will need to bring some files and data from the iMac to the laptop, not sure what method will use... but may use a manual method from Time machine if possible.
You can migrate your files.. this works well for most people.. but the disk size in the laptop might be SSD and small in which case yes, manually copy the files.. but don't use TM .. if you need to copy files there is no reason to use the TC at all.. the two computers linked over a network and you can copy files directly by sharing on one computer.