A common issue that arises on a regular basis. Home owner purchases a linear drain online and feels they saved a few $$. Now they hire a tile setter who informs them that the drain they purchased will not work with the selected waterproofing system. The majority of systems have integrated drains specifically designed for them. Hire your professional tile setter first and trust their expertise. This link will help. https://www.ceramictilefoundation.org/homeowners-guide-to-hiring-qualified-tile-installer

Do you really need more light over the island? Some people have enough recessed lighting that drop-down isn't necessary. Some people get balloons the size of the fixture they are considering and hang them down to get a feel for the space. You can also read up on standard formulas for sizing like from this article: https://www.lumens.com/how-tos-and-advice/how-to-choose-the-right-size-ceiling-light.html

Here is your room layout. The brown line indicates an 8x10 rug. If you add the 16" etageres they will land right on the edge of the rug and I'm not really sure there is enough room for people to sit and move around. As it is there is only 30" from the edge of the end of the table to the window and entry into the room. Once you add any table leaves you will be outside the room area. A 81" table can certainly handle a 48" fixture since it is so very open in design..

I think we only have one part of the question . All you will get here is hundreds of pics from beth and you still will not have an answer . Post pics of the space and the table . A pic of the LR so we get some clue as to your style and if you have a fixture you are considering post that. BTW all those are added in a comment here not new posts