I see the next validation in 4 days according to the website. As a 1st timer, does that mean I"ll have to wait for 4 days to start mining?
if you have passed the validation, no need to wait, turn on the online mining function and start earning 
I have a small question, is there a minimum hardware system requirement for the node and client to install on the VPS server ?
Please check here https://idena.io/?view=guide#guide-remote-0
Thanks for the answer ! I read, but apparently missed this