Confusion regarding remedying negative externalities of consumption through taxation
Your reasoning is basically correct. In fact, when I teach externalities to my students, I draw something very much like your diagram 1.

The textbook is confusing because the MSC and MSB curves are supposed to show the social benefits and costs of this particular activity. Taxes and subsidies can't possibly change these costs/benefits because they don't change the fundamental real effects of the activity (one unit of smoke is equally disgusting, regardless of whether it is taxed or not). The tax just means that in addition to this cost, some money is changing hands. But that's not really a social cost because the money will end up belonging to someone.



I don't think it's too helpful to start thinking about the idea "that a tax will also cause an increase in MSC (effects on employment of tobacco farmers etc.)" 

Those workers sell their labour in a labour market with a price mechanism. Unless we think there is some market failure in that labour market, the market achieves allocative efficiency. We don't usually talk about externalities when people loose out from price increase or quantity falls in a well-functioning market because those things are efficient and there isn't a very strong case for intervention.