Slight digression- keep in mind that if your modem doesn't have a battery, it won't work in a power outage. The special modems Comcast requires for their telephony all have batteries that last about 8 hours. Of course, if all your telephones require separate AC power, that doesn't matter (I have an old ATT phone as backup that runs off the minimal power available over all phone jacks).
After trying for most of a year, I finally was able to buy and activate the correct modem for Comcast digital voice (Arris TM722, available at Best Buy for $150, must be purchased through in-store Comcast rep). They now charge $7/mo rental for an obsolete modem I figure I'd paid for after the first year or two. The higher cost of internet-only and additional services I've gotten used to through the Comcast telephone service (like email sent to me transcribing voice mail, and call logging and blocking) kept me from going the Ooma (or similar) route. Your questions are basic enough so you might consider the same, unless your home-based phone is not so important to you any more and you can put up with problems. One reason they charge rentals is to make it trouble-free for people who don't want such hassles.
I found your questions a little confusing-- if you don't have a wireless router now, I'm not clear that you need one unless you're expanding your capabilities at the same time. It might have been better to have specified how your current equipment is connected-- how you get iPad internet, and how the PCs are connected to the internet, and what you want different. The Comcast digital voice modems have minimal connection options; my old one did have a USB port the new one does not, but that's about it-- I think one LAN, one phone (two jacks, I think for 2 phone numbers).