1. How do I add a node to a segment by clicking in the spot where I want it?
2. If I break a path in 2 separate lines (but still the same path), to turn them in 2 separate paths, how can I choose only a line and hit ctrl+shift+k without going through selecting all of the nodes in that line?
3. Can I toggle the colors between line and fill of a shape?

Thank you very much!!! I'm only beginning with IS, but I hope I'll stick around for a long time

1. If your using a recent version tehn just double click on the line when in the node tool. a point should be added at the spot you click that doesnt affect the line shape.

2. switch to selector mode (can be done by hitting space) before doing the ctrl+shift+k. should do what your after if I'm understanding you correctly.

3. Rightclick on the current style indicator in the bottom left of the window, then select "swap fill and stroke"

Tank you very much, you solved it! And the solutions are very elegant!

Another problem I had was selecting multiple nodes without box-selecting them. I found that if you roll the middle mouse button over a node, you select more and more nodes with the increased spin

Again, thank you very much!!