Fragmentation of mesh

This is my first post on this forum, so hi!
I’ve quite new at blender, but I am learning quite fast (I think). I’ve made a test model of a character and imported it into Unity game engine, but it was importing very long and it stated that the mesh has too many vertices and had to cut it into fragments. My question is, how can I cut a mesh into smaller fragments? I’ve thought about making each part of body from different cubes/cyllinders, but I still need to join them in order to attach them thogether (e.g to merge vertices of an arm and body).
Also, on a side note: is there any reliable way of smoothing model, without using subdivision modifier? Or can I somehow add modifier only for a part of the mesh?

Thanks in advance.

if you like building your base models out of primitives, but desire a single manifold mesh, you will want to use the retopology tools ( mesh snapping ) to build an optimized mesh over your original.

Lasso or Box select a part, press P to separate it into a new object. However, if you want to keep the smoothing continuous, the mesh has to be manifold (one piece).

You have smooth shading turned on? If not, select everything you want smoothed, and click Smooth under the “shading” header in the toolbar on the left. You can have both Smooth and Flat faces in the same mesh, you can also use an Edge Split modifier to define either angles or seams that you don’t want smoothed.

How many subdivisions are you using? Generally 2 is good, anything above 4 starts to get overkill.

There is no way to use the subdivision modifier on only one part of the mesh. You can use the Loopcut Ctrl-R tool to do highly selective subdivision, if you feel like you want one section to be smoother (or more detailed) then Loopcuts are an important go-to tool.

If you’re talking about a sculpted model, the Decimate Modifier can work as a quick and dirty way to cut down on the polygons. It’s nowhere near as clean as retopologising by hand as Modron suggested, but it is a lot simpler.