The battery in the ol' XF has trouble handling all the crap I have running, and with anything else I add it is only gonna get worse...
Would installing a second battery fix this problem or is it more complicated than that?

Do you want this to help supporting the load with the engine running or not running?

Get an optima or odyssey battery, use 0awg cable for earths and power and you should be fine.
Actually no, get your alternator checked out and upgraded/replaced if necessary, then go the new battery.