That second cable looks like one for a satellite PVR install, not Virgin Media.
As for the other questions, I think you've got an isolator, Splitter and attenuator in your current cable setup. Out of the three you might be able to get rid of the Splitter in the middle without it causing problems, although to be honest, if it all works I'd generally leave it alone!
As for a wall box for the isolator, here's an option
https://ebay.us/ABA9tA. Anything past the wall box I'd leave running free in case it need to be replaced at any point.