1> I have read on another thread the need for an IDP when driving. I will be driving out of Barcelona but I do not know what this is....help much appreciated.
2> Should we prepurchase tickets to the various Gaudi sites [ Including Sagrada Familia] in advance.? What about the Miro and Picasso museums?
travel dates Mid April and renting an Apartment.
TIA

IDP = international driving permit. A translation of your drivers licence - used in conjunction with your drivers licence.

Prebook Gaudi sites - absolutely. We were there in April last year and there were crowds everywhere. If you hadn;t pre-booked, you didn't get in to many.

Are you an AAA member? If so, see: https://www.aaa.com/vacation/idpf.html

Are you also planning on visiting the National Museum of Catalonian Art? If so, you might want to buy a Barcelona Art Ticket (Museum Pass). It costs 30€. I believe general admissions to Fundació Joan Miró, Museu Picasso, and the National Museum of Catalonian Art are each 12€. We bought Barcelona Art Tickets online, printed out our receipt and validated this at the first museum we visited, which was Museu Picasso, where they exchanged our receipt for the Barcelona Art Ticket, a little passport-like booklet. Then we just walked right in, unlike the many people who were standing in a long line to buy tickets.
Barcelona Museum Pass - ARTICKETBCN

I agree that you should prebook the Gaudi sites. When you book Sagrada Familia, you'll also be given the option of visiting a tower.

I don't know how much time you'll have for Barcelona, but other Art Nouveau sites worth visiting include the former Hospital San Pau complex, which is a 10-minute walk from Sagrada Familia:
https://www.santpaubarcelona.org/en
And Palau de la Música. This is a concert hall and alternatively, if short on days for taking tours, you can attend an evening concert instead.
All guided tours | Palau de la Música Catalana
These were both designed by architect Lluis Domènech i Montaner
https://www.barcelona.de/en/barcelon...-montaner.html

I am not a member of AAA but get my IDP there, so you pay more than AAA members.

>1 As answered above

>2 For the Gaudi (and Domènech i Montaner) sites, I would! If you won’t be upset if you can’t visit specific sites or have to stand in line unnecessarily, then your call. I didn’t find it necessary to prebook either the Miro or Picasso museum in late May.

You should definitely book in advance the Gaudi sites, or use a local travel agency to organize a guided tour for you. Tickets sell out, and queues in high season can be huge...