A Mac Air 13" will do everything you want, just keep in mind that you will need a small connector cable to connect a VGA or HDMI cable to the Thunderbolt port. There is no built in VGA or HDMI connector in a Mac Air. The newer Mac Pro models do have a built in HDMI connector but unless you are planning to do some high-end graphic work or similar you won't need the processing power of the Pro. I have several colleagues working with the 13" Mac Air (I have a Pro myself) and it is a great piece of kit for all sorts of office work. We use Office 2011 or Office 2016 on these Macs, I have not used Keynote myself.