According to USDA bacon should have 120 parts per million of added nitrite. If it's "dry-cured" ( water content reduced significantly ) it can be 200 PPM.... but for standard bacon, 120 PPM, is the USDA standard...
The math is easy really, and I would strongly advise having a scale, it makes things a lot easier and more precise.
Math... 120 PPM, is the same as 0.012%. So, you add 0.012% nitrite to make bacon. Since cure #1 is 1/16th nitrite, you need 16 times more cure #1, than the amount of nitrite needed.
for 1000 grams of pork belly, you need to add 0.12 grams of Nitrite, to get this using Cure #1, you multiply that by 16, which tells you need to use 1.92 grams of cure #1 per kilogram of pork belly, to make pork belly bacon... ( along with other salt, sugar, and whatever spices you want )
How much salt or is it sodium, or how much sodium is in salt?
I Have no idea how much sodium is in salt... but I do know from experience that I like bacon made using roughly 2% salt. (whatever amount of sodium that adds up to )
If you want to do it without a scale... For every pound of pork belly use.. 1.6 teaspoons of Sugar, 1.47 teaspoons of salt, and 1.1/8ths of a teaspoon Cure #1, and 1/4 teaspoon dry spices ( like pepper ). That will get you pretty close... but I'd encourage you to get a scale, it's much easier really.