As ceady stated, if you're only wanting to add lighting control to a single room, the URC option may work better. If you have plans to expand into a more whole house HA scenario, don't go the URC route. UPB is a good choice and it is easy to accomplish what you're after. Per your PM, a simple plan would include purchasing the UPB dimmers that you need (pay attention to load ratings). I use and have sold many HAI dimmers but I also really, really like Web Mountain's stuff. You will also need the room controller (some think of it as a keypad) with IR receiver. I am unsure if the IR codes that work with HAI room controllers (which I can get to you to program into your MX880) also work with other manufacturers' gear. You may want to look into that if you go with other gear. Lastly, you will need a PIM to program the UPB links into your dimmers. The UpStart software used to program UPB via the PIM is free to download at a number of different sites and there are countless threads at Cocoontech in regards to programming. There is no need, yet, to purchase and install a more robust automation controller (a la Elk or HAI Omni).
I am on the clock now but, will look at your other questions later and it's likely that someone smarter than I will answer in the meantime.