Epoxy grouts resist staining much better than conventional grouts. And, while I am not trying to talk you out of small tiles, be aware that you can get attractive non-slip tiles in any size. We just did a re-tile of our master bath that involved replacing 2"X2" tiles with 2'X2' porcelain tiles, and there is no slipping issue at all...even in the shower. And the difference in maintenance is amazing. Another point to remember is that certain materials, including some natural stones, are more porous than porcelain, so sealing them regularly may be helpful to minimize staining in a bathroom.

I‘lol comment on the “quality” aspect a little. My previous house had tile throughout the main living areas and it was laid on the diagonal. Initially when we looked at (&bought) the house we too thought it was different/special/unique/whatever. Friends commented on it looking nice. However, it just really sucked. Rugs and furniture placement always looked bad bc it was hard to get them lined up with the angle or exactly perpendicular to it. It quickly became a PIA. It never just blended away as a floor. I know yours is a bathroom but I would still rethink it. It could easily end up looking like you just couldn’t make a straight line. Maybe use a smaller rectangle tile for herringbone or another interesting layout or find some interesting tile and do a stacked or offset pattern. I think you’d find it nicer and less “unique”. Sometimes unique is the equivalent of bless your heart.

There will be a transition between the two floors so ultimately it would be your call, keep in mind improper instalment does void manufacture warranty. Typically you go across the joists when it comes to warranty purposes.

We bought the American Standard. Unfortunately, we haven't had it very long, so I can't tell you how well it holds up long-term. I can tell you that in our previous house we had a small powder room before a remodel and the smaller size toilet that we had to have in there failed (was replaced) twice within about seven years, so there might just be a design difficulty with smaller toilets that causes them to not be as reliable. We had a Kohler and an AS in there. Toto is a premium brand, so I understand why you're interested in it. 24" as the previous poster indicates for clearance is a minimum and sounds too small for me. Put a chair in the room and try sitting and standing from it when it's placed 24" from the far wall and see how it feels to you.