for a good staking how much coins must buy??

As many coins as you can afford.
Yes that is true, however if he wants to stake daily then I would suggest at least 50k to 100k RAIN. If weekly then the minimum amount should be at least 5k to 10k. The more the better but as some people can't afford much I think 5k is a good start and right now its a good time to buy while the price of RAIN is under 1k sats.
I know vella, you mentioned it a couple of times before.... I am talking about blocking to get rewards more regularly. This
ACTUALLY means putting them on different addresses on the same wallet, right? The amount of rain you're staking depends on the amount you're holding. So do you think reducing the absolute rain amount per address and the reduced stake-rewards are overcompensated due to increased frequency stakeing s when everything is summed up?
You can send to the same address if you want to separate them into blocks. They just need to be in individual transactions. ie. you send rain to the same wallet address twice instead of all at once.