Questions about Object attachments and Joints

I made two objects and put them on my feet.

If I join the two together will I still be able to put them on both feet?

Do I join the two objects at the edges? If I overlap them will I have a seam?

If you join two prims, are the still two prims or one prim?

i) Cool

ii) You can put them on both your feet by making a copy of one set, but they'd be two sets of linked objects. If they were shoes, you'd be wearing 4 shoes. People typically attach a right shoe and left shoe to the respective feet respectively as separate objects. How you define 'shoe' is a different matter tho.

iii) How you link objects is entirely up to you. If you need them to be seamless, learning how to use the grid snap might help. A linked object can be composed of prims which have gaps in between them. They don't need to lap.

iv) Objects are composed of 'linked' prims. The prims within it will always remain as prims, and you can unlink them later as well. You can't technically 'join' things to become one entity yet in SL.

I would add that if you overlap them, you won't exactly have a seam.

But you may have what is known as "Z-Flutter." You've seen it, I'm sure. SL doesn't know which texture to render on overlapping prims that occupy exactly the same space, so it alternates between the two of them, very rapidly.

The way around it is to match the textures perfectly, so it doesn't matter which one is being rendered. SL still does it, but since it's alternating between two identical textures, it doesn't show.

Not really applicable to shoes, but just in case you want to build something else.