How do you all determine the power level of your adversaries?

In D&D and Pathfinder and such you have a CR, which, while not always completely accurate, gives you a good baseline from which to start. There are no CRs in Genesys. Yet, as we all know, not all rivals or nemeses(?) are created equal.

You can't take your hot off the press jedi and expect them to be able to compete with Darth Vader.

According to the rules the best dice pool you can expect a nemesis to have for a skill is 5 yellow and 1 green (6 attribute 5 ranks). Leaving aside boots and other things.

So, what are the guidelines y'all use for adversaries at the beginning of a campaign vs 50XP, 100XP, 200XP etc?

It’s all feel to be honest. It depends on the number characters and what they are good at, the environment, the starting range, then the abilities of the NPC’s is important too, and their weapons

A single combat focused character can comfortably handle a minion group of 5 if the encounter is in their favour, say it’s a melee focused pc and they start at short range. But those same minions with long bows starting at Extreme will probably knock the pc out.

I would start with an encounter with 2 basic minion groups of 4, and perhaps a rival standing back as reinforcements.

anything with Soak 5 or more is usually a real challenge

any time there are more NPC initiative Than pc slots it will be a challenge.

but also be aware that a TPK is quite hard to do, especially if the bad guys have a reason to take unconscious characters prisoner

Also, it is easy to ramp up a challenge if the players are dominating a battle that you intended to be climactic (which has happened more than once to me).

Despairs are a great opportunity to introduce new minion groups or a rival. Or flip a GM story point for the same effect.

You can flip 2 or 3 story points to really change the environment or scope of the battle. The earth opens up, an unstoppable enemy horde crests the distant hills, the BBEG reveals a character's loved one is captured and in jeopardy. Used infrequently, this is a great way to increase the challenge level of a big encounter without simply throwing more adversaries into the fray.