1. In LA you don't have a contention, so you don't need to worry the same way about making sure your points link back to it. You don't have arguments, and you don't have contentions. People structure their LAs differently, depending on what they like. In my opinion the most effective topic sentences are those that identify one noun and one authorial attitude towards that noun (which can be expressed in terms of desired reader response towards the noun). The paragraph then shows a bunch of things the author does, and each sentence finishes with how that thing demonstrates the attitude you've identified. So, what they did and why they did it. Finishing everything with a general link back to the overall topic of the piece - or, heaven forbid, a general statement of "therefore encouraging the readers to agree" or the like - is repetitive and unnecessary.
2. Again, it depends on your BP structure. The Assessment Report last year said that *meaningful* comparisons were beneficial. You can integrate the texts in every paragraph, or you can have a few meaningful connections done in another way. It's flexible. There are over 40,000 students sitting the exam, and they won't all do it the same way.