I own an 880 and have no knowledge of Prontos. The 880 is in my view a good mid-range universal remote that balances medium cost with good features.
Specifically on your questions. * The 880 allows operation of devices in two main ways: as Activities or as individual Devices. Activities turn mutliple things on, and set correct inputs. Switching to another Activity can turn off devices not required, or not as per your choice. The Device menu enables you to operate any device individually - on off, change inputs etc. My guess is that you would use your lights as a device independent of AV equipment. Some people do switch on lights with Activities and leave them on until the global Off button is pressed. * The 880 is programmable using the Harmony website; which is often love/hate. After a while, I found it quite easy to use and adequate for my needs. It learns missing IR commands just fine, although the library is pretty good. * The 880 will allow different layouts in the sense that you input all devices in your house and then set Activities that use the appropriate collection of devices. Seems to me that you will have a 'Watch kitchen TV' Activity that simply turns on that TV (and off again.)
