If Farage wanted an exit he would stand down altogether - him standing in Labour marginals will strengthen Labour's position as he splits the leave vote.

He will simply campaign for a harder Brexit than Boris can deliver. Only no deal will work for him and there is no chance of that happening.

I think too much is being made of Trump - he is very likely to be out of power in 2020. Only Bernie would have any empathy with Corbyn amongst the leading American candidates. Guarantee Biden, Bloomberg etc would have exactly the same view of what is best for the UK and it wouldn't be Corbyn.

No deal can definitely still happen.
Assuming that Boris gains the overall majority that he craves, either with Tories or, more likely with some form of coalition with The Brexit Party, they (the coalition) will simply negotiate in a fashion that hacks off the EU, ensuring that they cannot negotiate a Free Trade Deal by the deadline at the end of 2020, at which point it will be a case of "see ya later" and we WILL leave with no deal.
The moderate majority, will need to do everything possible to prevent this from being possible.
IF Farage ends up holding the balance of power, which is certainly a strong possibility then, anything can happen.

The Brexit party will not win a seat - if Johnson wins a majority he could use it to turn the tables on Barnier to get a better deal - EU moved when they thought it could happen until the Benn act gave them back the power.

We have been terrible at negotiating with the EU - May didn't want to leave and she was a disaster - just like anything she touched - a firmer stance might work better.

What exactly do we want

We want the UK to negotiate from a position of strength - something it has failed to do to date.

To achieve what though, there must be hundreds of permutations of Brexit - I struggle to see exactly what we want. My understanding of the referendum was that a leave vote was for quite a hard leave, but no one seems to be able to define what it is we’re looking for.

My understanding would be:
Free trade no tariffs
No free movement
Protection for existing EU citizens in the UK and UK citizens in the EU
Remove ties to ECJ - ability to make our own laws
No financial contribution to the EU

You're for a hard border in northern Ireland then? It's a legitimate position although not one I'd support.

Free access to the European single market (I'm interpreting your "free trade" here) will take some negotiating with those priors but after a few years we should be able to get a deal.

I remember seeing someone early on in the whole Brexit thing, describe our position as being in the EU but wanting to behave as if we weren't, then being a non-member but wanting to behave as if we were. Your list is pretty much that.

I think that your hopes fall down on "Free trade with no tariffs", primarily because we (the UK) would also like to negotiate independent trade deals with the rest of the world.
Interestingly, why would any nation, currently trading with the EU, wish to rock the boat by offering the UK a better deal - we necessarily have to be offered something not quite as good as the EU are achieving.

The elephant in the room would still remain "the Irish border", something utterly neglected by EVERYONE during the referendum, although Boris does now seem happy to chuck N. Ireland under the Brexit Bus.

The real reason behind Brexit could be a significant tightening of the laws surrounding how businesses legally hide their cash to avoid corporation tax etc.
There was a really interesting piece on this on the BBC website earlier today but, it seems to have been removed / disappeared.
If I can find it I will put up a link.