OO lets you apply style attributes at different levels of generality: the whole document, all the rows of a given level, an individual row, some specific text in a row. If you select a bit of text in your outline and call up the "Style Attributes" inspector, you'll see a nice little list of all the attributes applying to that text, arranged from those that apply most specifically ("Selected Text") to those that apply most generally ("Whole Document").
The important point is that the attributes set more specifically (the ones at the top of the list) override attributes set more generally, if they conflict. You pasted in formatted text, and the formatting applied to text overrides the formatting set for the row, level, and document containing that text. That's why some things aren't changing when you apply styles.
In the future, I suggest using "Paste With Current Style" instead of plain "Paste".
As for the outline you're trying to clean up, I think the thing to do is, (1) MAKE A COPY (in case this is bad advice I'm giving), (2) select all the rows in the outline and select "Clear Style" from the Format menu. This will (I think) clear away all the formatting except what's applied to the whole document. Then you can select "All Level 1 Rows" in the styles pallette at the bottom of the utility drawer and use the Inspectors to set the formatting of your top level rows, then select "All Level 2 Rows", etc. etc.
I hope this helps.