You can lay tile directly on a plywood countertop, but if it’s a high-traffic surface in a kitchen, it’s better to add a moisture-resistant base. Plywood is susceptible to moisture, so if dampness seeps through from the surface around the sink or where you prep food, it can cause the plywood to warp, leading to grout damage, cracked tiles, or mold growth under the surface. 

Yes, it’s possible to cut tile without a wet saw; instead, you can use an angle grinder, a glass cutter, a snap cutter, tile nippers, or a rotary tool with a tile-cutting blade. A manual tile cutter or snap cutter works well for the larger tiles that wet saws are typically used for, while smaller projects might just require nippers or a glass cutting wheel. If you’re working with large quantities of tile, however, power tools are best.

Yes, you can tile over existing shower tiles, but it's better to remove the old tiles first for the best results. Tiling over existing tiles requires a clean, level surface and proper adhesion. If the old tiles are in good condition, you can roughen the surface to improve adhesion. However, removing the old tiles ensures a smoother, longer-lasting finish and prevents potential issues down the line.

Larger tiles can be difficult to install because they’re heavier and bulkier than their smaller counterparts, which makes them harder to haul around and put in place. Plus, if you don’t install the tiles correctly, they could crack or break. For these reasons, it’s best to hire a professional for large-format tile installation.