Great choice of file name ! I haven't got many of them!

Use the offset function in the tool......

Agree, the button should be shaded/different colour dependent on state.

3D CAD requires a little thought, a bit more and there can be a post at the end also.

I leave that to the student.

Select the last feature in the tree, and in the properties set Refine flag to true.

Why do you make things harder than they need to be?

Place the first sketch carefully around the origin, centred is usually the best, then use symmetry to advantage.

I beg your pardon I thought I'd included it...

Just examine the file I posted, use the space bar to make the first sketch visible then the pad and so on.....

The dev version has a drawing aid that allows this in the sketch but it is not parametric so crap really YMMV.

You are a person that finds problems every where, a glass half empty person.

So....

It makes two solids... NOT ALLOWED!

Use a sketch like this:-