Suggestions for itinerary and transpo from LAX to Barcelona-Andalucia-Protugal

It's doable, but adding Portugal will make the rest of it a bit hurried. Connections between Spain and Portugal are not as quick, efficient or numerous as one would expect from looking at the map and extrapolating from the rest of Europe. Consider flying in to Barcelona and out of Madrid (or vice versa), saving Portugal for another trip when you can do it justice. With 18 days, that would give you plenty of time to hit most of Spain's top highlights, and without feeling rushed.

The order for Spain by train/bus: Barcelona - Cordoba - Sevilla - Ronda - Granada - Malaga. From there you could fly on TAP Air to Lisbon. It looks like the best way to Salema is by bus, changing in Lagos or Faro. It looks like that journey would take at least 5-6 hours. To do that: Barcelona, fly to Granada, then bus/train Malaga - Ronda - Cordoba - Sevilla. With a rental car, you have more flexibility between Sevilla and Granada. A lot depends on where you want to fly home from.

So it's possible to do such a trip but realistically you'll spend nearly as much time in transit as in sightseeing. First count the days you have in Europe. Do you mean 18 days including travel to Spain or 18 days in Europe? Assume your first day is a non-day, you'll probably be in a sleep-deprived, jetlagged haze after an overnight flight. Unless your return flight leaves in the evening, your last day will be just packing and going to the airport. So if you have 18 nights away from home, that's 17 in Europe and only 16 full days. With 8 destinations, that's about 2 nights per place. You'll use on average 1/2 day just moving, so you'll have one full day and maybe another 1/2 day in each place.

So, indeed, adding Portugal is too much. When are you planning to go?

To add to David's advice about flying into one city and home from another, these itineraries must be calculated using a multi-destination search function. They are not a set of one-way tickets.

I have never been to Salema, but several people have reported here that it was disappointing--apparently over-touristed rather than charming.