You are brave, I could never let someone tile anything, unless I was able to check the layout daily! I hate the look of 1/3 offset, so I prefer to go with stacked when there is no other choice. I find the repeating stair-step pattern busy and prefer the straight simpler lines of the stacked pattern. You need someone to do a scale drawing of the layout to get a feel for how the patterns will work. Next best thing is if the tile installer will prop some tiles up in the different patterns and take some photos for you. Match the grout to each tile color. Good luck!

Deflection of joists/subfloor is a structural issue and how much a tile can deflect before it cracks is a structural & stone/tile industry issue, both outside our specific expertise, but when we face this issue on one of our projects we will work closely with the tile manufacturer/supplier, tile installer, and structural engineer to ensure it is addressed. Some common approaches are beefing up floor joists &/or subfloor, narrowing spacing of floor joists (which reduces the subfloor span thus beefing it up), & lowering the floor joists/subfloor so thick set mortar bed can be used (the weight of which will require beefing up the floor joists. If a structural engineer is not involved but the deflection limits of the tile is know and the design/construction team is familiar with span tables for joists/subfloor (some included in the building codes, but specific industry standard & product data for materials is freely available online) and deflection calculations (which is simple length divided by a specific factor, then calculations can be made to beef up the joists & subfloor to adequately limit the deflection. I'm fairly familiar with such tables because I will use the tables &/or a joist/beam sizing software called iStruct in my design process. I like to determine the approximate joist size/spacing for a project long before I'm ready to involve a structural engineer & certainly long before the joists & subfloor are engineered by the lumber supplier, which is common in residential in our market (instead of using a structural engineer) & doesn't happen until after a contractor has the construction contract. Code required deflection limits are fine for flexible materials. The limits basically just ensure the structure will never fail - they don't ensure the structure will never sag. For instance, the code required deflection for an 18' wide garage door header/beam will result in the header sagging .9" if L/240 is allowed, or .6" if L/360 is allowed (sorry, I don't keep which L/ is required where in my head - I have books for that) - that much sag is visible to the naked eye. I've had lumber suppliers tell me they will not sell a garage door beam sized to code minimum deflection because they will get callbacks from unhappy home owners who see the sag & fear it might collapse, so to sell a "serviceable" beam as they call it (serviceable meaning don't get calls from upset owners), they will use a much tighter deflection limit like L/480 or L/720 to limit deflection to an amount not visible to the naked eye. That' basically the same issue that needs to be addressed with tile/stone flooring - the floor structure might meet code, but is is "serviceable" for the specified floor finish. this quick google search brought up a few links that appear at first glance to specifically address this issue - it looks like L/720 is a common deflection target for stone floors instead of code required L/360: https://www.google.com/search?q=stone+deflection&rlz=1C5CHFA_enUS725US725&oq=stone+deflection&aqs=chrome..69i57j0.2618j1j1&sourceid=chrome&ie=UTF-8

Tough for anyone to offer much of anything then. Also it should be on them to clean somehow as anything you may do to the floors will end up on you as in he washes his hands as you worked on the floor. And whoever touches it last......................

I think I have that same 10” hex from Spain, except mine is the charcoal color (looks black). Just wanted to say I love it, and i think the grey version looks good with your vanity. Also, if you’re pricing marble tile it’s worth taking a look at www.thebuilderdepot.com. Our master bath has a ton of Carrara Venato marble tile- 4x12 on the floor, herringbone mosaic on the shower floor and 6x12 on shower walls, and we sourced all of our tile from them. The prices are amazing compared to the tile store where we bought the rest of our tile, and the marble quality is great.