You will need to go through a fabricator (or tile-setter) for installing a porcelain slab. I recommend getting an estimate for installation cost before placing an order. The fabricator can help you determine if one slab will be enough.

In California, there is only one specialty license for both tile-setting and fabrication. I don't know if this applies in other states as well.

When porcelain slabs first became available, there was a lot of breakage, but now that they are available in 12mm (1/2-inch) thickness, not as much of a problem.

That is going to be priced higher than using a modest granite for that. It's extremely fragile in transportation and fabrication, so the labor is appropriately high, for a high risk. It also requires very expensive tools to fabricate and handle it. This isn't something your average tile setter can do. It takes specialty training, and only the very few top guys in the market will be up for taking that risk. The material cost is the absolute cheapest thing about the job.

The mitered corner of any stone/porcelain product is its weakest point. Not as much of an issue in a bathroom, but still a risk of getting a chip there.