Land is the expensive part.

Project management wise, depends if you have any experience in it and your only building one you could do it yourself. Although without any experience in the building industry I would advise against it as workmen tend to get fucked off big time if the required materials aren't there.

It's always best to get an architect to design every aspect of the house (obviously you can sketh what you want it to look like and they will take it to the next level). It will help with building regs/suppliers etc. I know of a few people who have handed over drawings on lined paper that have been done with a pencil and ruler

Architect's are very expensive but their work is worth it. Im not sure on project managers, on the last project I was on we were paying him £550 a week on a subcontract but i couldnt tell you how much a freelancer would charge just a normal person on such a tiny job.