Flush them until the runoff is pretty clear. Get yourself a PPM meter. If you bought bagged soil they likely won't need any feeding for most of veg. Also check this book out, it's a good reference book. https://www.amazon.com/Steps-Grow-Cannabis-Complete-Beginners/dp/173519610X
I started with Mr. Growit's book. A good succinct starting point. I then went on to Ed Rosenthal's book and the Cannabis Grow Bible by Greg Green. https://www.amazon.co.uk/dp/173519610X/ref=cm_sw_r_cp_apa_glt_fabc_E56GSGJBS8XY9V3C1MQ4
https://www.amazon.co.uk/dp/0932551467/ref=cm_sw_r_cp_apa_glt_fabc_GK66VPJ4D2GX6H8WK9MX
https://www.amazon.co.uk/dp/193786636X/ref=cm_sw_r_cp_apa_glt_fabc_FHQQ3ABJFY6B30B9Y1AH
Amazon Mr grow its book 7 steps
Not at this stage. Early veg they want high humidity. This is a pretty good book to keep on hand as a reference guide. https://www.amazon.com/Steps-Grow-Cannabis-Complete-Beginners/dp/173519610X