Starch and press before you cut. After cutting you want to handle the cut pieces as little as possible.
My advice: Make a practice block. That way you can test out the pattern, get familiar with the pattern, AND measure your seams. Depending on the pattern. a 1/4" seam may matter or it may not. It is nice to know what the seam is though.
What pattern are you doing? You might get pattern-specific advice that way.
Have fun don't fret, and show us pics.
As for the thread, I use beige or light grey for the top and the bobbin. Depending on the color of the block, I may use up bobbin thread and take a "devil may care" attitude.