I have done some of the same ports....my advice, and purely my opinion.
I'd take theships tours for Florence/Pisa...WHY? When I was on the Royal Princess in May 1997 (a similar re-positioning itinerary), many passengers boasted that they were going to take public transport and save the money. We took the ships tour that dropped you off and picked you up 8 or 10 hours later. When we go to Italy, there was a public transit strike. Now, I know you said that you were not going to take the public transit, but...the cabs then had free reign to charge whatever they wanted.
Unless you have booked/arranged something ahead of time with a reputable independent tour company, I would stick with Princess on Livorno and Paris (done the Paris tour from La Havre 2 times with Princess).
Barcelona, you could take a cab and be fine from my past experiences.
Gibraltar, no tour necessary you can walk to the tram to go up the rock.
Neveer been to Cadiz/Cassablanca
Lisbon - fantastic city, pick pockets are rampant so be careful. We hired a cab who did not speak much English and didn't take American Money but we pointed and he go us to the top of the mountain and we walked back. Lovely....
Enjoy...looking at Europe for May...may see you on board...
