All you are really going to need for sure is fluid. You'll want to drain and fill it when you install it. It's not a bad idea to get a clutch kit at the same time. With that many miles you have to be close to needing a clutch if you have't replaced it already. The kit will come with a pressure plate and disc, and will normally come with a throwout bearing and a pilot bearing.
There is not really much to have someone check on a manual trans. There is nothing you can really see from outside without taking it apart. You shouldn't have much problem with the replacement, they are pretty good transmissions.
No, there won't be any surprises. You will find the replacement very easy, it only takes a couple hours on a hoist. If you let me know if its a two wheel drive or four I can get you the instructions.
Here is the clutch replacement.