The Antronix ara4-7B1 would be a better amplifier than the RCA TVPRAMP1R. It has a decent noise figure and the ability to handle a lot of strong signals without overloading.
http://www.antronix.net/uploads/spec...A4-7B_61_0.pdf
Because you are going to keep your coax based internet and phone service active, you'll need to trace the cabling. Start at the internet modem. Does it have a phone cord connected to a wall jack? Traditional phone wire is one or more pairs of wire, not coax cable. When the cable company started competing with the traditional phone company, they commonly delivered phone service through a phone jack built into the internet modem. They then used a standard modular phone mounting cord to connect the dial-tone service from their modem to an existing phone jack and the existing phone wiring. But in some cases, the cable service may break-out the dial-tone with equipment mounted on the outside of the home... Regardless of which way your service is wired, you need to know which coax runs from the cable company's network to the internet modem so you can leave it connected to the cable company while disconnecting the rest of the coax cable in the house (for re-use in your separate antenna system). Be sure the cable company coax is not interconnected to your cabling that is fed from an antenna.
Tracing out each coax may be challenging if you can't follow it from end to end, but you should be able to easily figure it all out by disconnecting one cable at a time from the splitter(s), then confirming which TV or modem looses service. Take the time to confirm that only one TV or modem is affected, there may be more than one splitter in the existing system. Tag or label each cable as you go, putting every connection back the way you found it, careful to disconnect only one connection at a time.
Once you've done the tracing and labeling, you'll be able to know which coaxes can be disconnected from the cable company system and reused in your totally separate antenna system. I expect that you'll be able to reuse the Antronix amplifier and passive splitters, the cable internet modem won't need either if it's the only devise to remain connected to the cable company service.