Need input on a trip to Spain Spring 2020.

Barcelona is an exciting city and you can spend several days there and only cover some of the sights.
Uber is all over Spain.
The trains are good.
We took an excellent motor coach from Barcelona to Madrid.
It is not too far to stay by the beach and buses run frequently between the beach and downtown but downtown is more fun.
Where else you want to go in Spain will depend on your personal interests.
There many Michelin Star restaurants in Spain, including some in Barcelona.

just12 is correct about Barcelona. There is much, much to do in the city, and you could be happy there for a number of days. However, you are smart to want to go other places. Trains are very good as are the buses. there's a high-speed train between Madrid and Barcelona that we took.
For must-see places, I would include Madrid and Toledo. From there you can go south to Granada, Sevilla, and Cordoba.
Valencia is directly south of Barcelona and is another pretty city on the Mediterranean.
Or go west and north to Pamplona, Bilbao, Santiago de Compostela. Perhaps even into northern Portugal to Porto. So many places to go in Spain, it's hard to decide. Good luck.

Previous comments about Barcelona are good. We stayed for 7 nights and never ran out of something to do. Took Paella lessons, had excellent private guide for a walking tour of all the Gaudi sites. Madrid is splendid with excellent art museums. Trains are excellent. See as many places as possible without making yourself nuts!

We stayed in an Airbnb in both Barcelona and Madrid. We took the train between Barcelona and Madrid, which was very easy. The beach in Barcelona is in walking distance of most attractions; subway was easy too. Book your entrance to the Gaudi sites as soon as possible.

Strongly recommend you pre-book at the Picasso museum in Barcelona
Barcelona is a wonderful city - we were there for four days and want to go back.
Spain has so much to offer - we loved our time there. I'd pick a special interest (e.g., Roman ruins, art, etc.) and focus on cities that offer special sites. If you can go to either Granada to see the Alhambra or Seville (some distance) to see the Alacazar Real, the trip is worth while. Have a wonderful time!!

We spent a month in Basque and Catalonia - our favorite area in Spain. Barcelona, as many have said, is a great city with wonderful food and plenty to do. We also spent a few days in French Basque St. Jean de Luz before going for a week in San Sebastian, rented a car and spent three days in Rioja wine country on the way to Barcelona. We used FeelFree for apartment rental in SanSe and VRBO for our apartment in Barcelona. I would be happy to give you details of sites and restaurants, etc. if you contact me via email.

All of the responses above are right on target. Barcelona is such a wonderful city, you could easily spend four to five days there. But you should see more of the country. Take the high-speed train to Madrid. Another great city and quite different from Barcelona. But since you will already be in northern Spain, why not explore that area? Zaragosa, Burgos, Pamplona, Bilbao, and San Sebastian can easily take up the rest of your two weeks. As one of the responders suggested, you can even go into the Basque country of France. St. Jean de Luz is lovely.
The south of Spain is marvelous, but it's a long trip from Barcelona and deserves two weeks or more on its own.