1) The Roamio remotes can do both but it should auto pair and use RF by default. There are ways to manually set it to IR or RF. 2) Yes, older remotes work just fine. The new remotes have a back button but that is really the only difference. 3) Sure but if the Roamio remote is in RF mode there is no need to set the remote code (it only affects IR). You can set the remote code on the Roamio just like any other TiVo. However, you will have to use a non Roamio remote to do this easily since when it is in RF mode the remote code does not matter. 4) RF will work through obstructions (no line of sight is needed). So if you are using the Roamio remote, you will want to leave it in RF mode.