Hi creevyie
Short bits and pieces:
Totally agree with Ann: hohos in summer can be horrendous... long queues at the stops are the norm, especially near key attractions. The service is quite well staffed and you have many buses, but still, the number of tourists in the city keeps growing and growing. So, I always advise against using hohos as means to get from A to B, not only they're always full but they're awfully expensive compared to any other public transportation means -which, for those coming from cities where these are no-go, over here are inexpensive, clean, efficient and safe... pretty much all Barcelonians use them. You can purchase a T-10 travel card offering you 10 journeys on metro/train/bus/tramway in the city for 10€, and if you prefer an all-day unlimited pass, the HolaBCN card for 2,3,4 or 5 days is also cheaper than a day or 2-day pass with the hoho. IMHO hohos are good for spending 3 or 4 hours driving thru the city so you get a better grip on where most attractions are and also a glimpse of those other attractions you won´t be able to visit due to lack of time. Also, they allow having a feeling on different neighbourhoods of the city.
I also concur on the option to visit Sant Pau on your own. This is a city well used to receive tourism so most places, especially attractions, have information panels in at least three languages: Catalan -the local language, Spanish and English, and sometimes also in French. I grant you that a tour visit always brings a different "view" on the attraction, but still...
In general terms, I think your schedule is well balanced and perfectly doable. When I travel I tend to have my bucket list A and my bucket list B, just in case I can't do something on A, or for when I end up having unexpected free time between different visits. Given the sheer number of things to see in Barcelona, I would suggest you do the same...
About funicular in Montjuïc: don't keep your expectations too high on this particular one, it's simply a means of transportation but has no impressive or special features or views. Also, talking about Montjuïc, as I've mentioned before, it's a hill full or museums, stadiums and parks but no residential nor commercial premises.
When exactly are you visiting in August? From 15th to 21st you have the Festes de Gràcia, a festival of one of the most iconic neighbourhoods of Barcelona. They celebrate this year the 200th anniversary of this festival which has been going on almost uninterruptedly since 1817. So if you're around, I'd plan for a visit to the area. The programme will not be online until it gets closer to the date, but the official site is here: http://www.festamajordegracia.cat/ Expect music, popular lunches, castellers and other traditional Catalan displays of heritage (ie. ball the bastons: http://infocatalonia.eu/w/Vs39y , correfocs: https://www.youtube.com/watch?v=9iXROi2CJn4 etc, also in a junior version: https://www.youtube.com/watch?v=uPvdnL77vfk ) Among other things to see, one of the most visited is the Street Decoration Contest in which several streets of the neighbourhood compete to obtain the prize to the best decoration. Everything is done by hand by the neighbours, no commercial brands or anything... that's precisely the point: neighbourly friendly competition. See a video of a previous year here: http://infocatalonia.eu/w/FZHgQ A drawback though is the number of visitors... expect lots of them. Ah yes, no tickets, no reservations needed, as most popular folk festivals here, everything is free to attend.
Expect heat, a lot of it and humidity so don't plan for a too tight schedule because you won't meet it. This year is bound to be one of the hottest for a long time, at the beginning of June we're having already typical days of August.
Enjoy!