Hi Bob & welcome to the boards. Everything Fuzzyboots said is spot on (& usually is), however the only piece of advice i can give you is this: Despite its D20 origins MnM v3 is not D&D. Its focus is on the amazing, with things like hero points & the power stunting it allows. These mechanics (along with the complications system on the villains side) lead to a game where there is no such thing as a formula scale for encounters.
MnM is a group community story telling game rather then a GM versus Player slug fest that D&D is. As the GM of a MnM game you can win every single time, by building perfect villains capable of obliterating PC's, but thats not your job. Your job is to challenge the characters & supply them with a compelling plot line.
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