Sardinia itinerary quick check - beginning of September

There are a lot of short stays and so it really depends on what you want to do--if you like a fast pace and can only see what you want to see by moving, then go for it. If you just want to explore, then you could do it from fewer places and save a lot of time moving and checking in and out. I stayed in Cala Gonone for five days and wished it was double--really, so so much to do in just that area! I am not implying all stays must be that long, just that fleshing out your specifics for each stay would really help us and you evaluate. You for sure do not have room to add Bosa.
I think you could make a good case to merge at least two of the northern stays.

Unless your main reason for this route is visiting beaches, I would change it up. I’d add a day to Santa Teresa and take the ferry to Bonifacio, Corsica. A great day trip, from Santa Teresa. You could visit the beautiful beaches on Capo Testa.
4 n on Madelena seems a lot. After San Teodoro, I would drive to the west coast to Alghero spending some time there and visit the Grotta di Nettuno. Then head south through Bosa to Oristano. The nearby Area Archaelogica di Tharros and Capo San Marco are beautiful. From Oristano you could drive to Villasimus with a stop at Su Nuraxi di Barumini an excellent UNESCO site.

I’d consider staying a night or two in Cágliari. It’s an interesting city with some wonderful sites. Check your car rental agreement. I saved almost $100 by returning my car in Cágliari rather than the airport which is a short train ride away.

Thank you both. Just to make sure - this will add a few 3 hrs drives to the itinerary. In your opinion - worth it? I will then revise the itinerary.

It may depend on if you wanted to drive the Orientale Sarda, which is on the east coast, but I did not suss out the entire drive that was suggested. I'd lean toward fewer stops, not more, but you have to weigh your own preferences. If you cut some time on Maddalena then you have at least a day to play with, but it is always nice to have a four-night stay at some point on a trip of this length--laundry gotta dry in addition to the enjoyable down time.

So I will have something like this:
Santa Teresa Gallura,2,30m drive + 20m ferry
La Maddalena Island,3, ~3h
Cala Gonone,3, ~2h45m
Alghero,2, ~1h15m
Bosa,1, ~2h45m
Villasimius / Costa Rei,3, ~1h15m to Cagliari Airport

Is this better, makes more sense?

I thought the drive from the airport to Santa Teresa Gallura was more like an hour, and I would not drive much more than that on arrival. It's a windy road, easy to zone out.

I've replied to you over on TA. But I think your original idea of sticking to the east coast (except for Santa Teresa) is fine. You could add all the other places suggested (and many many more) but you can't see everything anyway. Extra time spent driving is not fun time in my opinion. Why drive further to see places when you've got nice places to see without driving further??
Anyway STG is about an hours drive from Olbia and no need to use the ferry to get there.
From STG to La Maddalena it's less than hour to drive from STG to Palau and then you get the ferry over to La Maddalena

it was supposed to looklike this
Santa Teresa Gallura,
2,30m drive + 20m ferry La Maddalena Island, 3,
~3h Cala Gonone, 3,
~2h45m Alghero, 2,
~1h15m Bosa, 1,
~2h45m Villasimius / Costa Rei, 3,
~1h15m to Cagliari Airport

Its just too much driving I feel. Asking if I only have 15 days was my original itinerary ok with just hanging on on one side. Is the night allocation ok. I do see the comment to reduce La Maddalena to 3 and will do so. Am I missing anything inland close to my route?

I agree--it's a lot of driving. You have to accept you will miss a lot--once you do that, you will find it freeing. I would strive to get a bit of beach, a bit of town, some mountain time, and one of the archaeological sites if you are so inclined.
I would not try to include north, west, and south in one trip.
How do you like to spend your days? We drive when it is to get somewhere we cannot get to otherwise, and aside from that, we want to be doing something like a hike and minimize moves. I say that not to say "be like me" but just so you get a sense of where I am coming from and prod you into feeling what you would want to be doing. It's really hard to go wrong though--so rest assured you'll get there!

Im trying to break the drive from CG to Villasimus. Is Nuoro a good place for 1 night or you can recommend a better place. Yes I completely understand I miss a ton, with heavy heart. Just don't want my husband to drive more than a few hours. For your idea of town/beach and mountain, any favorite places you can advise on?

Well CG to Villasimius is under three hours and that is the spectacular Orientale Sarda that I referenced, quite an experience.
Nuoro is great but it was the hardest place with a car if that matters. It really felt like the heart of the island and we were glad to have included it. There was a little place we did not have time to check out but sounded intriguing called Urzulei, and that would be right off the road. Baunei is also along this road and it was a cute little place.
If you want to bypass the SS125, then Nuoro or a nearby village would work.
Tough decisions, I know--I am already planning a return visit!

Ca you Please elaborate on 'it was the hardest place with the car' :). like getting there or driving the narrow streets or parking?

More the parking, a slightly more tricky ZTL than we’ve encountered elsewhere, lots of one-way streets. We’ve driven in a lot of places and it was just a little hairy, but worth it! We picked an apartment on the edge of town but did not resist the temptation to drive through town a couple times too many.
I would not avoid it for that reason, it just came to mind.
The drive up was surprisingly tame, and I am not a great passenger on mountain roads.
Really fantastic restaurants there too.