Soak the noodles in a bowl of warm water until soft enough to separate, about 10 minutes. Mix the fish sauce, sugar, chili sauce and lime juice in a separate bowl. When the noodles are soft, drain and return to the bowl. Put the bowls and other ingredients next to the stove (this dish cooks quickly).
Heat a wok or large skillet over high heat until very hot. Add the vegetable oil, then add the shrimp and stir-fry until pink, about 2 minutes. Transfer the shrimp to a bowl using a slotted spoon; leave the oil in the pan. Add the garlic and tofu to the pan; stir-fry until just golden. Add the noodles and 1/4 cup fish-sauce mixture; stir-fry until the noodles absorb the sauce, about 3 minutes. Add up to 1/4 cup water if the noodles seem dry, but don't let them become mushy.
Add the radishes, scallions and 1/4 cup peanuts; toss to combine. Stir in the remaining fish-sauce mixture. Taste and adjust seasoning (you can add more water, lime juice or fish sauce).
Return the shrimp to the pan and heat through, about 2 minutes. Transfer the mixture to a platter; top with bean sprouts, jalapenos and the remaining 1/4 cup peanuts. Serve with lime wedges.