{Upsides
Government actually takes note of what voters say}
Nothing to do with being in or out of the EU.
{Sterling likely to devalue which makes exports cheaper to others.
Imports become more expensive so internal demand for UK produced goods and services increases}
Handy except that food being one of the major necessities will go up.
A significant amount of UK industry is actually EU (or other country) owned, so their profits will fall. Failure of JiT will kill some off completely.
{UK can implement trade deals directly whereas at present they are governed by EU}
While this might be an interesting theory, in practice most things the UK wants are already traded through the EU and they will be involved (through WTO ruling) in most new deals.
{Subscription to the EU will end (deal or no deal) which is worth Approx 9 Billion per year}.
While true, it actually represents around 0.7% of the current UK GDP, about twice as much as the whole of the UK fishing industry combined IIRC.
{UK might be able to reduce, or even avoid, paying the 39 Billion}
The £39 Billion has already been established as the outstanding payments for ongoing activities, and a 'projection' to the end of 2021 (the original proposed end of a transition period).
{Stricter controls on future immigration}
It has always been available either by actually doing what most in the EU already do, or through 'emergency' provisions. When several countries joined a while back, there was a 7 year 'pause' in entitlements put in place by many countries. The UK didn't do this.
Failure to actually use the 'tools' available within the EU must not be blamed on the EU. While playing unfairly, the UK COULD have been far more draconian in letting EU citizens in, for which it would have been taken to court, and after a few years the UK might have had it's wrists slapped, by which time other mechanisms could be deployed.