Not familiar with specifics of your car, but according to metra EX/SI come with an amplified system so if that's correct you already have a stock amp either under the drivers seat or under the center console. (more details)

This gives you an option to keep that amp and just have 4 RCA plugs. Here is a thread on 8thgen of someone doing that. (thats how i did it for my RSX using a couple of these and a splitter)

Otherwise you'll need another amp to go between the speakers and N7. Hiding a headunit somewhere is also an option.

This could also change with how your existing sub/amp is connected, but i'm assuming that your current amp is just for the sub.

Now the N7 details.

If you want things like flash drive/backup cam you'll probably have to go with USB On The Go + powered hub + Rom that supports that stuff. I think your only option for 13 is Timurs rom. ( He wants money for it, but as far as i know its the only one that can do everything on 13. I have the first gen N7 with autodroid on mine) There are also a bunch of examples with parts people used on the bottom of that page.

Bluetooth and XM i'm not sure about. Technically you can get bluez for 13 N7 but if you're not comfortable around code I would not advise to go that route.

One option is to wire up a bluetooth/XM device in series with N7 so the sound bypasses N7 but then you run into issues of volume difference/control if you're using a stock amp.