Place the calamari into a bowl with the lemon juice, and let sit for 30 minutes. This will tenderize the calamari.
Preheat frying oil to 375 degrees F, either in a deep fryer or a large cast iron pot, no more than 1/2 full.
In a medium bowl, whisk to combine the flour, cayenne, paprika, and salt. Add half of this mixture to another medium bowl. Place the buttermilk or milk in a third bowl. Place the three bowls on the counter in the following order: spiced flour, buttermilk, and spiced flour.
Remove the calamari from the lemon juice, then dredge each piece in the flour, shaking off any excess, then into the buttermilk, shaking off the excess, then back into the second bowl of flour. Repeat this process with all the calamari.
Fry the calamari in batches for about 2-3 minutes total, until golden brown. Then drain on a paper towel and immediately salt the calamari generously so the salt sticks. Serve with marinara sauce and lemon wedges, if desired. Enjoy!