Some cable companies will actually GIVE you amps and install them to ensure that you are using equipment that does not disrupt the rest of the cable network. Never hurts to call and ask.
Use the best quality cable you can find (at least RG6, but if you can splurge for the RG6 Quad-Shield, even better). Also, use quality crimps on cabling that you do in your house as to avoid leaks of signal. If you are worried about the cable company getting mad at you for your own wiring, just use quality materials and do everything right (good crimping technique, no leaking signal, no open ["unterminated"] CATV
jacks, etc.) you will be OK
. Around here (and I'm sure most everywhere else) the cable companies use Thomas & Betts Snap-n-Seal connectors, which are more expensive but high quality. If you look on eBay, you can find deals on that stuff all the time. I picked up a crimper for like $30 (it was a knockoff, but the real Thomas & Betts tool costs like $100-150) and a coax wire stripper for like $10.
As for two cables running into a room, nowadays that is often a setup for satellite dish, but back in the day a handful of cable systems had two different feeds, especially in areas equally in-between two major cities. Or on the drop from the utility pole to the house, I've noticed that the cable companies have installed double coax so that in the future one of the conductors goes bad they can just wire it over quickly without having to run another drop. Or they can use it to dedicate to a cable modem.
Don't install a cable modem past an amp, that tends to lead to more problems than you started with. If you use a splitter to split off signal for a cable modem, only use one that is good to at least 1000MHz or higher. Often cheaper splitters stop at 950MHz which is OK
for analog TV
but can be problematic for cable modem and digital cable. Happy cabling...