Yes, given we're likely to be trading less, or at less favourable terms, with the EU then we will need increased trade relationships elsewhere. Relationships we now have to build from almost nothing as we have no current trade agreements outside the the EU pooled trade area.
Currencies do fluctuate. The market is trending towards the Pound moving from being in the $1.45 area to around $1.25 or lower - with fluctuations around those figures. If the Bank of England cuts the base rate further to encourage borrowing to keep economic activity up, then we are likely to see further downward pressure on the pound. Parity with the Dollar is being talked about, but I suspect it will be somewhere below the $1.2 mark.
Perhaps, over decades, we may end up with a stronger pound, but historically when you look at the exchange rates, the pound has never fully recovered value from major downships.
Of course, the issue here (as it will be for many others) is "if the Government needs to find another 15% on the current order for 138 F-35s then where is that additional £2bn going to come from?" Taxes or Cuts. And that is just one line item of government business.