The only way I can think of doing anything that has a continous face would be with a fit spline.
I don't think there are on features, etc... that will merge faces into a single surface, howevere there is a heal edges, but I don't think that will do what you are looking for.
Sure. You can delete the faces and use the "patch" option to fill them back in.
Since this is somewhat sketchy, depending on your edge geometry, you may need to delete faces in a more uniform way. For instance, let's suppose you have two edges merging into a single edge and you want to apply a steady radius to all three. You cannot do this because the "fork in the road" with the edges that separate as they fork from the single edge. You can split the faces in the fork region (to remove them), add the fillets you want to the three edges (with fork area deleted), then fill the surface back in as a single surface. Use tangency and contact options to govern your edge tangency and you have a clean surface instead of many fractured surfaces.
This is complicated to understand in a single post. Let me know if you'd like any help with something in particular and we can deal with it via email.
Basically this is a scanned femur. There are 4 main faces, non of them planar, all curvy. The part is solid though. I get trouble trying to cut-extrude holes in when they cross the face seams.
Perhaps you could knit your surfaces and use the new knit surface as the stop for your feature. So if you want to "cut up to surface", you would then choose the knit surface you created to properly stop your cut. (Same for an extrusion.)
![[pc2]](/data/assets/smilies/pc2.gif "[pc2] [pc2]")