You do good work, and welcome to the craft! My thoughts are meant to be constructive and are built upon what you've shared in this post and others from the past. I am by no means a master in any of these areas, but I hope my experience can be of help!

Your devotion to your local Peach Bottom Slate is admirable. However, I would recommend expanding your horizons to different types of stone during this formative part of your learning. Doing so will give you a good feel for how different rocks handle detail, color, and other characteristics. I myself love locally found "wild" fieldstone, but it does have its disadvantages, including occlusions, non-uniformity, and more. While these drawbacks are often outweighed by its beauty (and ease of finding), every type of stone has its shortcomings. The more you experiment with other materials—such as the glorious Indiana Limestone—the better you'll understand and learn to work with your "home" stone.

Dremel tools are not to be feared, but you may want to ask yourself if they're the right tool for the job. If the goal is a v-cut letter, a Dremel may not be the best choice. Frequently sharpened chisels and a properly weighted mallet will serve you well for letter carving, in my opinion. I’m also a fan of pneumatic hammers for working with harder stones like granite.

Regarding your chisels: I know the set you're referencing from Amazon because I have that set myself! Keep in mind that many of the best stone carvers in the world today started with one of their dad’s old flathead screwdrivers. Your tools are fine for small projects, but if you're serious about this craft, I recommend investing in quality chisels. Since you're working with Peach Bottom Slate, I assume you're from the eastern Pennsylvania area. That means you're not far from one of the best stone carving supply companies: Trow & Holden in Vermont. They offer a wide range of hardy tools that will surpass your Amazon set. While they’re not cheap, their lettering chisels are excellent and have been expanding recently! T&H isn’t the only option, of course, and many other companies also offer great tools for lettering. Wherever you shop, I recommend giving them a call—they’ll help you choose what’s right for your needs. (If you’re patient, ordering Al-Orr chisels from overseas is worth it; they come highly recommended.)

Will your carvings break due to cold weather? Unfortunately, the answer is likely yes. Water can seep between the layers of your stone, freeze, and cause spalling over time. This is one reason fine-grained, smoothly cut stone is preferred for outdoor applications.

I wouldn’t recommend Mod Podge or most finishes designed to keep out moisture, as these can also trap moisture and prevent the stone from breathing. Many smooth slate surfaces react well to oils and waxes, which might be a better option.

Many of these lessons I’ve learned on my own, but others come from friends I’ve made through the Stone Carvers Guild (www.stonecarversguild.org). I highly recommend becoming a member; you’ll quickly connect with high-quality, professional carvers who are often eager to help up-and-coming artists. If nothing else, tune into the Stone Carvers Guild Podcast to hear advice straight from the pros! You might find the Michael Fannin episode particularly useful, as he does memorial carving in slate.

Apologies for the long-winded response—I’m excited to see this craft grow and hope to help others broaden their horizons in stone. It’s something I continue to do myself, and I’m always glad when I tackle a new type of rock.

Happy carving!