I spent far more of my professional career designing telephone equipment than I care to admit.
It's a world of rather bizarre acronyms, which make it hard to find what you're looking for unless you already know them. An "FXS" port supplies power and can drive the phone. Its counterpart is an "FXO" port, which looks like a phone, ie. it plugs into a phone line.
"SLIC" is "Subscriber Line Interface Circuit", and there are various options depending on how long a cable you need to support and which countries' line interfaces you need to be compatible with. Fortunately a US line uses an impedance of 600 ohms, which most devices will support.
The one potential issue you've not yet mentioned is ring-trip detection. When the phone rings, its ringing circuit draws a modest current, but this can potentially increase greatly when the phone is picked up (this is called "looping the line"). Your line interface needs to detect the increase in current which occurs when the handset is lifted and must shut off the ringer very quickly, to avoid blasting the user with a very loud noise and potentially damaging something. There are generally two methods, called 'ac' and 'dc' ring-trip detection, and you may want to choose between them based on whether or not your interface maintains 48v dc even while it's ringing.