A:AnswerRoku can take your smart TV and change it to a monitor on the world. Virtually, everything available on the internet will be open to you. The smart TV is severely limited in its applications.
A:AnswerYes. I can use the remote from the 1st floor of my house while the Roku is upstairs in the play room without any issue. The remote is working on RF not IR so line of sight is not required.
A:AnswerMake sure you are getting 4k content to your TV. Even some TV's that are 4k require you plug these types of devices into a specific port for true 4K. Easiest way to tell would be with your netflix account. If you can see Dare Devil or House of Cards with the 4k logo, then you are truly in 4K.
A:AnswerProbably the biggest difference is the 4 supports 4K and will upscale 720P and 1080P content to 4K SUHD. The 3 will not. Big difference on my Samsung TV. They also improved the remote control a bit. I purchased the 4 to replace a 3 I had for the up-scaling capability.