What is the base gear requirement for fighting this guy though? It feels like I need some really good gear but the game doesn't do a good job explaining how to get better gear... or anything else, really.
The game doesn't really have gear checks. It comes down more to your ability to dodge or parry while still putting out consistent damage. I haven't fought him since the most recent patch so there could have been some rebalancing but I'd say for the first Falstead fight being level 3-5 with tier 1 gear is totally fine. You'll want a few more levels for phase 2. If you're struggling with phase 2 you can save it for later and come back at level 11+ with tier 2 gear to make it much easier. But those are just some very broad guidelines based on my own personal experience.