I would have thought even the longest of Ws (Tenerife?) from a base much further away than NCL would require just a single crew, no hotel expenses etc, and with modern aircraft and high maintenance standards you shouldn't be factoring in potential costs of engineering support because why anticipate technical faults when the risk should be minimal anyway?
I think "Boundless Optimist" might be a more appropriate user name with those comments!
You can't operate even NCL-PMI-MME-PMI-NCL within a duty day, let alone NCL-TFS-MME-TFS-NCL. If you are operating the back half of the pattern, MME-TFS-NCL, the start time of the duty is such that you're unlikely to be able to fit in road transfer from NCL to MME before the first sector and still complete the two sectors in the allowable FDP. The crew picking the aircraft up at MME would need to road in the day before and overnight.
You could potentially operate this with no engineering cover. It's probably pretty foolhardy to do so on a long rotation with EU261 liability if it goes wrong even once out of a 26-week season and - in the case of PMI - with passengers connecting to the Marella cruise ship.
And