Elections

When voting in the Centuriate Assembly to elect consuls, did the individual Roman citizen vote for a single candidate, or did he vote for two (one for each of the two consulships)?  Similarly for the four/six/eight praetors?  Is there evidence?

There's no certainty but we know that a candidate was selected when he achieved a 50% vote, so in other words, it was 'first past the post' and if necessary a second vote was called to select a second vacancy. It might well be, for practical purposes, that voting for consulships were separate anyway.

I can't find anything definitive in primary or secondary sources either.  Livy (26.22, 27.6) indicates that each century announced two winners, but nowhere does anybody say whether individual voters submitted one name or two.

Roman voting did not work as modern versions generally do. They worked on the principle that a small vote was taken, the result carried forward to a higher level as a block vote.