I replaced my hydroboost unit (along with my master cylinder) on my 2002 GT back in 2016. It really wasn't that difficult. Just follow the instructions above. I was able to get a brand-new Motorcraft hydroboost unit on Amazon for not too terrible of a price.
I discovered mine was leaking because my power steering pump started whining from low fluid level, and there were no leaks at the rack. I didn't replace my power steering pump (until last night, but that's a part of a 3½ year long project on my car, where it's been up on jack-stands in my garage all that time!), but it was fine.