1.) There will be no delays at Dover because even within the customs union, there are still waiting times at the border between Switzerland and Germany.
2.) Border staff will not be overwhelmed, because ultimately they are there to act on intelligence gathered by the police. Border staff are not checking each container for signs of incorrectly labelled beef. These checks are performed by individual consumer protection agencies, usually at the factory.
3.) Food will not become more expensive, because the government has the power to set tariffs on EU imports. And, importantly, without EU rules on third country imports. The UK has the power to lower tariffs on food from outside the EU.
4.) There will not be a crisis in Northern Ireland. The EU cannot (physically) force a border between the two countries, unless they invade. The issues of drug smuggling and people trafficking are not the true concerns of the EU, because they are in charge of organising these crimes, just like every other government, including the UK. The border issue is something designed to annoy the public, the people behind the scenes are not in any way concerned or frustrated.
5.) The fishing industry will improve, because British fishing vessels will finally have access to all the fish in British waters. And not just what's left over after the French, Dutch, Norwegian fishermen have taken their share.
6.) Food quality will increase, because smaller farmers will be able to compete with the monopoly conglomerates who were once supported by Common Agricultural Policy subsidies.
7.) Innovation, particularly in the tech sector, will rise. The European Patent Office is a cartel protectorate, that attacks software development companies and uses predatory lawsuits to steal their patents. Without the EPO infringing on British business, the economy will thrive.
8.) Lower numbers of foreign students will mean less upward pressure on rents, less downward pressure on part time wages and fewer jobs for the university propaganda industry.