Maybe this is more of a personal style question or maybe it's a question which could lead to overall document size.

I have a couple of 300+ page documents I'm going to have to edit soon and non of these documents have any styles, multilevel list numbering, TOC, or any type of formatting other than simple left aligned paragraphs with manual type numbering.

I have setup a template which I will apply to get everything squared away, but curios about which is better or most efficient: spacing between lines?

Should I go with line spacing of single or line spacing in exact or at least etc. The document font will be TNR 12 if that makes a difference.

Also, how can I change all paragraph marks between each paragraph into the normal style without applying the normal style paragraph mark one by one between paragraphs. This is another clean-up project I'm working on.