Are PPC necessary, if my 50 keywords are comes at first position in SERPs?
yes if you need to run ads it's necessary
if all your keywords are at 1st position then you no need ppc
If your website is getting good number organic traffic then no need to worry about PPC.
Continue...
But, If you want to make leads or conversions then I would recommend to do PPC.
it's depends on upto you because top 3 is ad's the may get chance to get lead's so...
If you want to make leads or conversions then I would recommend doing PPC.