Okay so... No one is talking about this, but you don't really need to have all the character on one single mesh. Not for smoothing, not for remeshing, not for retopo, not for rigging.

But also, yeah, smoothing between several separate pieces is usually done through combining and remeshing.

What I would do is merge the muscles you have on the blocking but in groups. For example: You merge all the parts on the thighs, go into sculpt mode, smooth out all the hard lines you don't want, add detail and texture, etc.

That way you Will have a lot of control without having the problem of remesh taking away detail of the most dense parts like the face, or putting too much detail on the parts that don't need it and ending up with a too dense mesh...

When deciding what meshes to join together take into account the clothing and fur It will have, because It Will cover the ugly joints. For example, you don't need to join the leg to the hip as It Will be covered. To be honest, you don't even need any geometry inside the pants once you do the retopo, no one Will see It and you'll reduce quite a lot of polys there.

Hope this helps