how much ADA should I stake to earn 1 ADA ? how frequently is made calculation of new coins to my wallet ?

Figure the average return right now is around 4.5% APY +/- you would need around 2000 to earn a little over 1 ada per epoch (every 5 days) average

FAQ for staking delegation rewards can be found here

Epoch period is 5 days, you will see your first rewards 15 -20 days after you first delegate due to the initial offset. You can see a #rewards faq at the link below

You always stake everything in your wallet, anyway. Rewards are paid every five days.