Well your mechanical abilities is rather important. This isn't changing your spark plugs here. You need a significant amount of tools, a sheltered work space, a very clean environment so you don't contaminate any internal part, the time to dedicate to this since it won't happen in one afternoon, and an engine hoist is a most. It's very important to stay vary organised and I can't stress this one enough. Every bolt and nut has to be kept track of and it's very important to know what wires go where. Replace any and all seals that are tampered with during this operation whether or not they still look good. You don't want to get all done only to find out something is leaking and have to tear everything apart again. In general with a used engine it's also a good idea to replace any of the higher wear parts like the water pump and serpentine belt while you have easy access.
If you've done an engine job in the past or at least will be working with someone who has, you know this already, but I don't want you going into this blindly since if you fail and have to take it to the shop anyways, their price will climb quickly once they have to clean up someone else's mess. To be honest, unless your a highly skilled mechanic with dedicated facilities, I'd still have the pros do the work.
