Hi mazehavoc,
Where will you store your pot for the winter ?
Is that the 5 gallon pot in the photo ? Looks more like 1 or 2 gallons ...
Did you just buy the tree now ?
Is dirt missing at the top of the pot ? ( roots may dessicate ).
Are you in a rush to propagate that tree ?
A fig tree that you just bought potted in a small pot is more likely to be in poor condition.
It will take a season of decent cares to recover.
I would asap pot to 4/5 gallons now for the tree to have more dirt to protect the roots during the winter. I don't like the look of the top of the pot ... but could be from pic .
Come next March, I would cut as you plan ... Although I would make it different.
My way would be to cut at 2' or 3' (3' for me) and remove all lateral stems.
That will force the tree to push several stems together come next season. You would then let 3 or 4 ideally spaced, from each other, grow.
That would be the new canopy.
If you leave an older side branch, it will either pump all the sap and become the next trunk, or be abandoned or get less sap and become a weak stem.
You could cut now and root now. You just need the appropriate space to do that regarding light, humidity and heat.
Good luck!