Wanting to achieve similar to …
https://www.designzzz.com/wp-content/uploads/2010/10/162-487x630.jpg
The skin modifier may do the trick.
https://docs.blender.org/manual/en/2.80/modeling/modifiers/generate/skin.html#bpy-types-skinmodifier
Once you layout your holes then you can apply your modifier to sculpt on it.
Alternatively you can add and subtract meshes using Booleans as well.
Side note:
Try playing with the 2.81 beta from the daily builds. https://builder.blender.org/download/
So in 2.81beta there is a better remesher that makes the workflow a bit faster.
My remesh settings may differ from your project. Adjust your settings to fit your object’s scale and polycount. You can undo and readjust settings.
Smaller the object, smaller the voxel size needed.
While sculpting, you can press CTRL+R for a quick voxel remesh.
What happens with the inside geometry? In 2.8 when you remesh a object that intersect it will keep the insides so the object is quiet a mess. Or did you use boolean union and then remesh?
Use Boolean modifier to make holes and remesh or dyntopo.
The 2.81 voxel remesher gets rid of the geo inside the mesh. Try it out and compare it with the Remesh modifier.
Most issues and artifacts would be due to nonmanifold geometry.
Example:
Suzanne is 3 floating objects
I just used CTRL+J to join the meshes.
As long as nonmanifolded meshes are fixed or the holes are covered, then it should be fine.
Refer back to my first gif to see how I made the holes. You can also Boolean straight through the mesh and remesh afterward.
Hopefully this has been helpful 
Thanks for the replies. I went for a simpler method, removing some polygons & bridge then smooth out in sculpt.
Hi!
I came across this thread also wanting to sculpt meshes with holes. Earlier I found a piece of free soft:
https://stephaneginier.com/sculptgl/
that allegedly can do this trick.
In this video the author shows how he punches holes through mesh and how the mesh automatically adjusts itself to his strokes:
However, I don’t know what exact setting he tweaks to enable this “self-adaptive topology”. Maybe one of you would work it out
The algorithm is based on this paper:
https://hal.inria.fr/inria-00606516/document
I’m posting it in case someone is interested in mathematical explanation of an algorithm that goes beyond what Blender or Sculptris can do (unless I missed something).
Trying to stick to Blender only but looks good.
I understand.
If you give this one a try however and will work it out, please let know