Pretty good for a first plan! [:)]

support columns are not aligned properly

Select them and change their Y coordinates, or use the Align... items in the Furniture menu.

staircases not looking good at all

If you deform them not proportionally, you'll get strange results. Beside this tip about staircases, the only way to get the staircase that fits perfectly your needs is to assemble some boxes, triangles and/or cylinders.
You might have to make some other decisions too, because the 3 feet wide spiral staircase you placed outside is probably too narrow. Why not placing there a simple straight staircase?

many overlapping objects - windows, furniture

What do you mean by overlapping?

Obviously it is not possible to approach any contractor with this little thing

It could be a starting point that will help you to communicate your ideas with friends and professionals. Now that you learnt Sweet Home 3D, you could try to design a second plan.