I want to make some small gadgets on a big shape,
The question in it self does not make sense out of context. We talking sotheing that aims games market or is it going to be rendered out? So whet is it going to be used for, and how does the rarget rendering sytem work. Theese are all questions thet you need to have a answer on before you even start to contemplate on such things as poly count. Without context such musings mnake no sense.
So theres several ways to do this depending on whta your target is, but one of the more fundamental things to understand is that theres no added value for having the objects combined into one.
So if your targetting, mentalray, maya software, renderman or vray for example keep it as nurbs, theres no reason you can not extrude and round the edges as nurbs, the quality will be better.
If games, then you dont need to make the hole necceserily as geometry at all, but in either case dont make a square pattern on the surface but rethare a round areound the hole so the hole starts form a radial.
Likewise protryudions dont need to be Cut on the underlying surface for games and many of the renderers, tough not reyes renderers like prman. But thenagain you use nurbs all the way anyway.
PS: if you smooth DONT talk about polycount as smoothing makes your polycount SKY HIGH in thsi case smoothging makes n^2 or n^3 times more polys than your accounting for!
PPS: polycount is not really an issue in most things. Only take it as it is whan it is.