Day of tour start in Barcelona recommendations

Rick's list of top attractions in Barcelona can be found right on this website at:

Explore Europe - Spain - Barcelona Just click on At a Glance.

You can compare that list to the tour's sightseeing itinerary and identify gaps. Choose things that align with your personal interests. I don't know which of the sights will be covered by your tour, but these are places for which you should buy a ticket in advance if you want to see them; their ticket lines are very long.

La Sagrada Familia
Parc Guell
Casa Mila/La Pedrera
Casa Batllo
Picasso Museum
Palau de la Musica Catalana (English tours can sell outi)

There are many other interesting options in Barcelona, but the others generally don't require purchase of tickets ahead of time. If you post here about what you've decided to focus on, others can confirm or correct my opinion about what needs to be done in advance.

After reading the itinerary of what's covered by the tour in Barcelona, I suggest:

Palau de la Musica Catalana
https://www.palaumusica.cat/en

Sant Pau Modernista Hospital
https://santpaubarcelona.org/en/

Eat dinner at El Quatre Gats, reservations required
https://4gats.com

Miro museum
https://www.fmirobcn.org/en/
take the funicular up Montjuic, see the museum and the go to the top of Montjuic for the view
take the cable car back
https://www.telefericdemontjuic.cat/en?utm_source=google&utm_medium=organic&utm_campaign=GMB

Because we read "Catedral Del Mar and saw the Netflix mini-series of Cathedral by the sea we took a guided tour of Santa Maria Del Mar, and enjoyed that
http://www.santamariadelmarbarcelona.org

The main Barcelona cathedral is also worth a visit
https://catedralbcn.org/en/

Lots more suggestions, what are you interested in?

Casa Batlio was not on the tour last Sept. I have not looked at the itinerary for any changes. We enjoyed our visit there.