I think he's a planner but not good in the real world. His people skills were obviously limited. He probably thinks everyone else is stupid compared to him, so the police might not notice the broken windows the bullets were coming out of.
Plus, in the immortal words of Mike Tyson’s ghost writer, “everybody has a plan until they get punched in the mouth.”
This guy probably had no real idea how physically demanding this was actually going to be on him. 60+ years old, firing multiple high-powered weapons at a high rate of fire, the room so filled with smoke it set off the fire alarms. He’d have been beaten up all to hell.
And maybe, just maybe, the reality of what he had just done finally hit him. Maybe he realized the atrocity he had just committed and in a moment of impulse, shot himself.
None of that precludes him having planned originally to escape. His suite was literally right next door to the stairwell, he had multiple cameras in the hallway. He had more ammunition and explosives in the car. Maybe he had a plan, but then he just got punched in the mouth.