I'm in the process of reconfiguring my home office to use the new iMac (due in about 7 days) instead of the MacBook Pro. I'll have to shift the 20-inch monitor & its desk-mounted post & swivel arm support because there's no way I'd use it as a 2nd display with a Retina display on the new Mac. In the meantime I'm using it as a 2nd display with the MacBook Air.
The iMac comes with the new(ish) Magic Mouse 2 & rechargeable keyboard. I'll give them a go but probably revert to the previous setup: A Logitech M557 Bluetooth mouse (designed to go 12 months on a pair of alkaline batteries) and the Logitech K760 Bluetooth 3-channel solar powered keyboard.