Before I answer, I have to tell you first, this is still Bill Vincent. Now that GW has changed over to houzz, it defaults to my houzz profile which is my company name, Creative Ceramic & Marble. Now, btnik-- to answer your question, I charge more on the floors, because it's a little tougher to keep the tile flush on the floor, thanks to gravity. On the walls, especially with a nonsag thinset, they pretty much stay where I put them. Only issue is making sure I shim them to keep the joints aligned, which is why I charge more for ALL wall installations than I do ALL floor installations. But in comparison to other floor installations, I will charge a little more for large format because of the buttering and scraping involved to keep the floor flat.

Yeah, there's not a strict right answer, so you just need to lay a few in each direction and see what you like. I tend to like them going left to right as I enter the room, rather than longwise -- if you're entering from a bunch of directions, then it basically doesn't matter at all. But you could lay a few out in the middle of the U and see if one direction or the other seems preferable to you there, which will be a consistent view.

IMO tub decks should not have tile on them at all. What is your countertop material? For example, our counter is marble, so all the rest of the horizontal surfaces are done in marble (the tub deck, shower curb, windowsill, etc). Is that an option?

To answer your question, no, the offset recommendation is not due to weight concern. The primary concern is lippage which occurs more frequently with large format tile (where one edge is greater than 15"). Minimal lippage is more frequent in larger tiles due to the manufacturing process. To avoid excessive lippage upon installation, a qualified tile installer will not only recommend the appropriate layout, consistent with industry standards and manufacturer recommendations, but use proper methods and tools (appropriate notch trowel size, mortar coverage, substrate prep, grout joint size, etc.) as well as consider the effects of lighting. Industry standards recommend any off-set pattern for large format tile to not exceed 33%. In other words, 50% offset is not recommended. Your choice of a stacked pattern would not be in conflict with the recommendation (it is not an "offset pattern"). Recommend you have this conversation with your professional installer as there are various considerations for a quality result.