What are the style requirements for pleadings in Arkansas?

It sounds like the rule you are referring to is for appellate briefs, in which case if you use a smaller font and margins the Clerk will refuse to accept the brief, and you would have to get permission from the Court to exceed any of the page limits. There isn't a set page limit on the addendum, but it rather would is included should be based upon its relevance to the issues. In Circuit Court a 12 point font and 1" margins are typical, as a stylistic matter you do not want to cram a bunch of stuff onto the page and make it too difficult to read.