Wretched Hive of Scum & Villainy
Because the conceit of this particular campaign is that it’s the “all rogue” game, naturally, magic will be quite rare. Honestly, after you’ve taken three levels of rogue, you are free to multiclass, including into a spellcasting class, if you wish.
This means magic levels will be quite low relative to what you may be used to from D&D/Pathfinder normally. I’m actually quite used to running in magic poor environments, including in modern magic poor or even non-magical settings. Most of the trick to getting it to work is proper pacing and challenging to make sure that you don’t need to use magic to be successful. And like I said, I’ve got a fair bit of experience with that, so I can manage that.
Although maybe it’s more a discussion for High Level, you won’t find many high level magic users as NPCs either. Most high level magic is done as rituals/incantations rather than as spells.