Small weekend painting jobs are fine for DIY, but when you're talking about doing the whole house in 2 coats, plus prep work, plus cleanup, you need to remember what its costing you to take time off work to paint... you are effectively paying your own labor by not working or taking annual leave.
Only other advice i'd throw in is if you hire a pro and plan on leaving any furniture or items in your house whilst the paint, wrap it up yourself.