Indeed, there is a lot to be argued over and some parts we will like, some we won’t, some agreements with farm trade will be very quick, the starting point is the tariffs we have now, many won’t change for a while.
What the EU will not allow, is us buying cheaper goods from elsewhere and then re export them to the EU. A good example is New Zealand lamb we import an agreed fixed quota at present and at the same time export 40% of our lamb to the EU, they will want to be sure we are not cheating on that agreement.
My guess is that will continue for a year or two, but any illusion that we can decide what we can import and export without reference to any third country is wrong.