You are in the business of solving customer problems, so I think it is money well spent to have both imperial and metric on hand. The first customer that comes back after you did a repair quickly instead of sending him elsewhere will pay for that extra set when he thinks of you first and not the other guy.
There probably isn't much being made in imperial any longer, so having a metric set on hand makes sense, but there is plenty of imperial equipment still being used that you need that set too. Maybe buy a basic set of each and expand as funds or necessity permit. I’m with you on the supply chain issues in the future, I can get most of what I need next day, but when I buy something, I buy extra to have on hand because I believe things are going to get harder to find, and more expensive.