#1 I think Clarkson's £144 profit was before subsidies.
#2 From what I see, farmers who know how to farm seem to make good money at it and buy up adjacent farms as the owners retire. Of course, they have to work at it and I expect that if they subtracted hours worked, the ROCE (Return On Capital Employed) for the business would be terrible.
#3 In the UK, offspring of farmers do anything from carrying on the farm to going off to university, starting a tech company and making millions.
#4 As with everything Clarkson does, there is a lot of cocking things up according to a script. However, he's very good at it and the show makes great entertainment.