Casa Lleo Morera is closed as far as I know.
Casa Batllo is an important site but was extremely crowded in August. It appeared that the owners were willing to cram in as many people as could physically fit. I hope conditions are better for you, because this is an expensive ticket.
Casa Mila has a lot of information about other Gaudi buildings on the top floor near the end of the tour, including brief videos of some located in other cities. If you're seriously interested in the modernista sites, don't skip this one and allow plenty of time. I think I was in there for about three hours and I could have used a bit more time.
Sant Pau was wonderful because there were incredibly few visitors there in August. It's a multi-building site, so you'll be outdoors for a bit. My timing wasn't right for an English-language tour so I used the audio guide. Be aware that the audio tour ends in the main building, where there's quite a bit to see. The map didn't make that clear and I almost ran out of time before I returned to the main building. Allow plenty of time.
Your list overlooks La Sagrada Familia, which I would consider a must-see and probably the #1 modernista sight.
MNAC (the Museu Nacional d'Art de Catalunya) has a nice modernisme exhibit in addition to other fine holdings, including frescoes and architectural elements from medieval churches. It's definitely worth visiting if you can spare the time. It's large, so focus on what you most want to see. There's also a small Museu de Modernisme located not too far from Casa Batllo. It can be visited fairly quickly. When I took the Tourist Office's Modernism Tour, we had a brief (roughly 15-minute) stop there. While I would have liked more time, I saw enough that I decided not to return for a second visit.
Because each site takes a good bit of time (usually a minimum of 90 minutes or more even if you pre-purchase tickets and don't have to spend any time in line), you will probably have to trim your list. With limited time I would skip the Casa Amatller, much of whose interior is pseudo-castle rather than modernist. I'd consider skipping Parc Guell, which is a bit out of the way, but I think others may disagree.
I opted to skip the Gaudi House Museum myself because guidebooks led me to believe that it was less interesting than some of the other sites.