You can, in theory, tile your fireplace hearth with most tiles. However just because you can, doesn’t mean you should. For example, it’s much better to use unglazed tiles because glazed tiles are more resistant to cracking under extreme heat. Porcelain is more heat-resistant than ceramic, but you can still design the hearth as you like by putting the most heat-resistant tiles directly under the fire and, if it matches your style, add more decorative tiles further from the center of the fire. 

While you shouldn’t use thinset mortar on its own as a floor leveler, it can work alongside other products to help level floors. For instance, you could start with a self-leveling compound, let that dry, then apply backer board with thinset mortar to help fully even out the floors ahead of laying tile.

The lifespan of bathroom tile can be 50 years or more, depending on proper installation and regular maintenance. A well-done tile job, whether it's a new installation or a retiling project, can last for many decades. To lengthen the life of your tile, it's best to have it installed by a professional and to perform regular maintenance. This includes routine cleaning, resealing, and regrouting as needed. With proper care, you can expect your tile to last 10 years or more before needing major repairs or retiling, especially in high-traffic areas where tiles can wear out more quickly.

Here’s another instance of where the answer is you could, but that doesn’t mean you should. Yes, part of the issue is getting the drywall to stay in place on the tiles, and it’s understandable that screws will crack the tiles and cause them to crumble. That’s why it’s a much better idea to screw drywall into studs, not your porcelain or ceramic tile. But aside from issues with attaching the drywall, it’s also about ensuring a smooth application without trapping moisture inside.