My and others' analysis of Minions turns up these general traits:
--Minions seem to be most likely made from Brutes, Soldiers, and Skirmishers as the base creature;
--Their damage is usually equal to the minimum normal damage of their type (if a "soldier" minion would have 1d10+4 damage from page 185, then their damage is 5; if their damage is 2d6+7, then 9 damage, etc.);
--Their hit point score is 1.
There are some variations in some minions, especially for damage, but I chalk that up to the idea that the Monster Manual was being written at the same time as development on the rules was occurring, and some variations slipped through.
There are no hard and fast rules yet, but those three tenets seem to make minions well within the ballpark of all known minions.