We don’t any recent experience with Brainy Filter. The last time it was also working without any problems.
2) The Product slider block itself is only a product slider – you cannot insert any custom text inside. If you mean something else, can you please provide a screenshot with some basic explanation, so we can be more useful.
3) Tabs/Accordion is a separate Page Builder block. You can put in each tab (accordion panel) other Page Builder blocks.
There are slider settings for each product listing block. Enabling a product slider, means that you will have only row with products. There is one more option to have a single product row without enabling slider with all extra products hidden.