I think it is too soon to tell.
If he lets people who know what they are doing run the government, things shouldn't be too bad. He can just tweet and stay out of the way.
But if he tries to get too involved in decision-making, I expect he will screw up something bigly.
I have a chunk of investment money on the sidelines, looking to get into the market if it goes down 20% in the next six months due to a foreign policy fuck-up.