The size of the tile has no bearing on the thickness of the subfloor since the weight is essentially the same. The larger the tile, the flatter the floor you want to have as lippage between tile becomes much more problematic. If you aren't experienced with large tile, you may want to avoid it!
The biggest thing with any tile is to ensure that the subfloor and building structure are sufficient to prevent deflection that can crack the tile since it is quite brittle. Ensuring full coverage is important as well, as any gaps can lead to point load breakage...all tile needs to be fully supported (you should get at least 90% full coverage on each and every tile and all edges with the goal of 100%).
Then, any bumps, dips, humps, ridges in the floor will be magnified by trying to bridge those imperfections. You really want to pay close attention to the prep and get things as flat as possible.
Some larger tile are also not flat, and end up arched or twisted during the firing process...some are as flat as standard glass...knowing what you have will make a difference in how you set things. The flatter they are and the closer in size (referred to as rectified if sized the same), the smaller the grout joint you can use, but the smaller the grout joint you use, the harder it is to prevent lippage (uneven height of an edge of one tile to another).
With that large of a tile, you'd have to know how flat the floor is, how flat the tile are before you'd know how deep the thinset would need to be. You may want to go with a medium bed mortar (often called granite and marble mortar) instead of thinset since it has more sand in it and supports large tile better while they set. Ultimate strength is about the same, it's just that they won't move as much in a medium bed if you happen to lean on one before it is set. Depending on the condition of the subfloor, you may need larger than a 1/2" notch...can't say without knowing the tile or the floor. Some tile have a waffle pattern on the backside, and require a bit more than one that is just flat as well depending on how deep the patter is. If the floor was glass smooth, and the tile rectified and super flat with no warps, cups, etc., you could get by with a very small notched trowel...but that is rare.
You will want to backbutter the tile that size to ensure complete coverage.
Lay out at least a box or so of the tile and check for squareness and consistency as that will impact the gap and mortar requirements.