Pete, for such an experienced businessman I'm surprised by this insistence that 'trading with the world' is like a tap that is currently turned off that can be turned on. Companies don't go to the government for permission to sell/buy their widgets from China or Brazil. If there's a commercial imperative they'll be doing it already. All a trade deal does is make that trade easier by either removing tariffs on that trade, removing non-tariff barriers, or ideally both.
There seems an indelible focus by Brexiters on tariffs, when the reality of global trade is that non-tariff barriers are far more important as they govern things like standards and rules. It's this that makes the single market so valuable because those standards and rules are integrated more deeply than any other free trade agreement in the world.
The rationale you're espousing is that we're going to substitute trading partners in Europe whom we've developed deep relationships with (on account of the above standard rules and processes) and suddenly jump in with partners elsewhere that we haven't traded with before (despite nothing stopping us), just because this basic belief underpins the apparent value of Brexit.
You also seem to be continually overlooking the fact that a) immigration is hugely important to the wellbeing of our companies, and there is not a single company that doesn't want to be able to attract whatever talent it wants, whenever it wants. If you promoted free movement from all over the world then you'd have a (very good) point, but you don't, you continue to bang the controlled immigration troupe, as though Windrush et al haven't shown the government to be absolutely bloody clueless at 'managing' immigration, and b) that immigration isn't hugely valuable to our society, and c) that this whole stinking shitheap wasn't all about immigration and getting rid of foreigners.