So I’m curious about which method is better for character modeling. I was trying with box modeling before but I was wondering if I could do merge modeling, where you combine different shapes together and remesh them into one object. I was worried about the amount of polys as I don’t want to have like 1 mil pols for said Remesh.
Whatever suits your abilities (which can only grow 
), system (computer), goals (low to midpoly or high poly detailed sculpt, game or VFX).
Obvious box modeling is older when computers where not that capable to operator with millions of polygons but it’s also “easier” to control the general shape and work towards more details. For sculpting you also need some graphical tablet to be able to add every littel grain of details and some experience with eye-hand-control (or some by far more expensive visual graphic tablet) .. but also a more powerful graphics card, CPU and lot’s of memory (RAM and VRAM).
So as always the answer to any:
..–question is: It depends 
I want to try Merge Modeling but I want to know how to remesh without too much polys afterwords.
The polycount is adjustable in the Remesh modifier. Just make sure you save before adding the modifier because if you set it too high, Blender will freeze and may even crash while calculating the new polycount.
In sculpt mode when pressing R you get a visual gagdet where you can select you mesh density:
Curves are often implying a lot of vertices.
And remeshing an organic shape with lots of curves is often implying defining a low value of edge length to retain details, that will produce a lot of polygons.
Basically to merge 2 meshes without remeshing with an high density of polys on the whole surface, you may use boolean modifiers/operators.
That may produce triangles or Ngons, not a topology only made of quads, like remeshing can.
Or you can simply learn to cut a mesh, separate it in several parts, rip its surface and then, to weld two surfaces, merge vertices of boundaries or to create an in-between surface by making more polyfaces, by bridging edge loops of boundaries, by filling holes.
So, look at tutorials about knife tool, bisect, loop cut, connect vertex paths, separate, split, rip vertices, merge, new edge/face from vertices, poly build, F2 addon, bridge edge loops, grid fill.
Then, you should be able to cut, split and merge surfaces with a low, medium polycount, properly and efficiently.
Remesh sets the polygon size to preserve the small details I want.
If the details are small, the overall polygon size becomes smaller.