You're screenshot wasn't attached...
The Find/Change can be pulled off and floated to wherever you want. On a dual screen set up, have it on the secondary screen.
For the sideheads, what are your settings in the Format > Page Layout > Column Layout... panel. Do you have multiple columns defined?
I have never seen the message "master pages have an irregular column layout". So, this is a pure guess.
Is it possible that you have some how connected text frames that have different settings for the side heads, for example, one off and one on OR side heads of different widths?
I would think that setting the side heads for one frame in a flow would set the side heads for all frames in the flow. BUT I vaguely remember having to turn on 2 columns for each frame in the flow to make the whole flow show 2 columns. But my memory may be bad.
Just a thought.
This could be indicating that there is a different type of layout on some master pages (you might not even be using them). Check if all have the same columns and if all have sideheads. Sideheads are a document level property, even though you can specify them at the text frame level.