Need more information: make, model, year, engine, and transmission; and whether you will be installing a used engine, short block, long block, or crate engine.

Obviously you are taking a chance with a used engine! I see they have a warranty but that's probably not going to cover labor. (I get a "not found" error when clicking on their warranty link.)

I'm not familiar with that specific vehicle, maybe Scotty or someone who has done this job can provide details. In general you would want to replace any wear items before installing it in the car. Timing belt if so equipped, timing belt or chain tensioner and guides, water pump, engine mounts, clutch if it's a manual transmission, etc. Basically anything that might be worn that's easiest to replace with the engine out of the car.