Yes, Trump is only trying to boost his campagin with LGBTQ voters. He has no hopes of winnning the Democratic California, but if he can convince a few queer voters in California that he is on their side, then maybe he can change the outcome in a swing state like Florida.
Trump is visiting LA because he thinks he has a genuine chance of winning the state of California. Trump actually stands no chance at all, because of California's very high Latino, African American, and Asian American populations. His trip there is a waste of time aside from the fundraising. But, Trump is running a totally new type of campaign where probably outcomes of his actions have little bearing on his behavior.
No, it is quite a stretch to make Trump visiting the Louisiana disaster zone "anti-LGBT". The man is a presidential candidate on the home stretch - it would be provocative and politically stupid NOT to visit Louisiana at this point. The governor and residents alike have expressed appreciation of Trumps concern, further underlining that the focus of the trip is the disaster rather than making some kind of LGBT statement.
No, Trump's visit to LA is not a way for him to support anti-LGBT rhetoric. This does not mean that Trump will not support anti-LGBT rhetoric while he is there. LA is typically a gay friendly city so it is not the right place for Trump to make anti-gay statements.