Question for you guys, do we need to backup the wallet each time after a reward is received or is the first backup enough to restore the current balance anytime in case of loss/corruption of the active wallet ?

I also just decided to buy some more RAIN from profits I made with another Altcoin. I don't have as much as you but I am working my way to at least 150k RAIN before the whitepaper is released which I believe to be very soon, hopefully be the end of the year. Once people start building on their stacks they will start to see the real potential RAIN has to offer when it comes to staking.

for a good staking how much coins must buy?? 

There is a tutorial for the raspberry. Join the slack channel to view it.

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.

I'm staking multiple coins on a VPS and it is working great

Suddenly getting this error trying to open the wallet. Anyone seen this? I excluded the folder from Windows Defender, no luck.

https://i.imgur.com/UHrbxON.png

I think your blockhain file is corrupted (first block is bad).
Try to delete the blockchain files and resync (backup your wallet.dat file always!) .
Did you shutdown your machine while the client is running ?

doing the same here- it is working like charm:)