How Much baking powder and baking soda should I add to regular ap flour??

Here’s another article!

https://food52.com/blog/8375-how-to-diy-cake-flour-and-self-rising-flour

King Arthur Baking says:

1 C. all-purpose flour
1.5 tsp baking powder
0.25 tsp salt

https://www.kingarthurbaking.com/recipes/homemade-self-rising-flour-recipe

Feel free to do an Internet search if you want a second (or third or fourth or ...) opinion.