Think my friends would call me a barn geek.
A few years back we converted an old (1780's) brick built barn into a house. It has turned out to be a nice home so I have no regrets at all, however the conversion cost more and took longer than building a new house from scratch. In addition we had to make a few compromises to work with the shape of the existing building. The windows are not quite the size, nor in the position you would choose if building from new.
I also have a "newer" (1905) building alongside that I'm just finishing off into a small workshop. Again, the work on this was expensive compared to putting up a new agricultural style building.
With all conversions you never can be sure how much money it's going to take until the work is underway and then it's too late to change your mind.
Not sure how regulations go where you live, however here if that lovely barn became part of a house, it would then become subject to a lot of expensive building code requirements. Keeping it separate may make it easier to retain the character that you treasure and also turn out to be the most cost effective approach.
What a great opportunity you have, however you decide to do it.