When all your devices are linked to the same account (same email address), then all the channels across the devices will be available. If you install on one device, will install on the others. (as long as the device supports that channel). If you remove from one device, will remove from all the others.
However, the layout is not the same. You need to physically arrange your layout for each device. (use the *button on your Roku remote and move the channels to the desired location). The Roku devices do not communicate with "each other" so they do not know if you relocated a channel to the top of the screen on one device. Generally though, if you arrange all your devices identically, then they should pretty much stay the same since all new installed channels usually get installed at the end of the list. This pattern should stay pretty consistent across your devices. (I have had the occasional channel install in the middle of the screen, especially Roku related channels that throws it off a bit). And sometimes a software update will occasionally move some channels around for some reason.
As for the question about resuming a program, that is channel/app dependent. Most have a Resume Watching/Continue Watching feature that allows you to do just that on another linked Roku device. (In some channels/app, the Resume/Continue is front and center, on others you may have to look in their menus a bit to find it. Some channels do not have this feature included at all. (I usually just pause and note the track time, just in case I have to fast forward to that point on another device).
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941