That XL lens is great.
My budget wasn't as high, so I settled for the lower cost 90/f8, rather than the XL 5.6 lens.
Now that you have the lens...go out and shoot.
As others said, shooting is the only way to determine if you need another lens and which lens you might need.
After shooting, you might find out that, as you said, that might be the only lens you need.
Do you have the rest of the kit?
focusing loupe, backs (lots of backs), good tripod, etc.
It took me a LONG time to gradually collect most of the parts of my kit. And I'm still gathering parts; compendium/lens hood, filters, etc.