Even if it is still Under Construction, there are some automatic machines hidden in Municipio station; but there is also a Tobacconist every 2 blocks and the 90 minutes duration of "Integrato" tickets start when you time-stamp them, not when you buy.
In other words, the old school is smarter than the new one and rows of ticket machines would be a waste of money. Do what Neapolitans do, Get a couple of 90 minutes tickets at the first tobacconist you pass by and use them when you need to. Un-used tickets will be a nice souvenir.
Since line 6 is closed, there are only 2 metro lines running within the city of Naples, that cross at Piazza Garibaldi and Museo stations. Getting lost is quite difficult.