The upgrade to w10 is pretty easy and painless and nothing gets lost, i put it off for months and months because i just couldnt face losing lots of passwords for sites etc, but was reassured by others that wasnt going to happen so took the plunge.
I did my laptop 1st and if that went ok i'd do the big rig, it went smooth on the laptop apart from having to manually get the synaptic trackpad drivers so i had my easy scrolling back again, so i upgraded my dual xeon beast after that, easy painless all my stuff is where i left it.
Vista was pants tbh, compared to XP it was stodgy bloatware, w7 was such an improvement.