none of the printers mentioned going to meet any of your requirements.

Prusa isn't fully opensource, but has the worst enclosed chamber printer imo.

Bambu isn't open source in the slightest (beside the slicer).

You are never going to print PC on a bambu either way, at least not Pure PC. Blends, sure, you need at least 100c chambers for pure PC.

diy kits are the way to go, but it is going take you a LONG time. a voron, ratrig, or annex k3 are your best bets with the requirements you want. each kit has their weaknesses, and most of them, are going to require upgrades from their BOM.