AutoCad 3D :: How To Check For Object Collision

I have some model boat plans (scanned images) and would like to convert them to 3D objects. I used a software img2cad for the conversion, and since the conversion is not perfect i have to redraw all the parts. So here are my questions:

1. For the parts i mostly used lines, splines and arc. What is the best way to join them, so later i can edit them to 3d solid object? I used join and it works well, however it creates a small angled edge at the end. (see image or zoom in dwg file).
2. For some of the parts the extrude command works only on the edges of the 2D object creating a hollow 3D object. How do i fill the inside?
3. In near future i would need to assemble all the parts and make the skeleton of the boat. Is there a way to check for object collision (if parts are too big for example to fit where they should)?

I also attached a file with two ribs of the boat as an example.