Preheat oven to 300°. Heat oil in braising pan with tight-fitting lid or heat oil in skillet, then transfer pork after searing in skillet to slow cooker or roasting pan with tight-fitting lid.
Season pork on all sides with salt and pepper, and sear all over in hot oil. Add lime juice, garlic, salsa, water/beer and cover tightly.
Slow-cook in oven until fall-apart tender in center (approx. 3 hours or 1 hour in instant cooker). Shred pork, mix with approx. 1 c of pan juices to season well. Taste and adjust, as needed.
For nachos, spread chips on sheet pan, add meat, then sprinkle with cheeses, heating until cheeses are melted. Top with desired additions: pickled jalapeños, avocado, sour cream, olives, lime juice, salsas, hot sauce and black pepper salt.