What will a lump sum grow to?

By compound growth: the amount multiplied by one plus the yearly return, once for every year. At 12% a year, money doubles in about six years and grows roughly tenfold in twenty.

If markets rise steadily, a lump sum does better because all the money is invested from the first day. If markets fall soon after you invest, a SIP does better because later instalments buy cheaper. Nobody knows which comes next, which is why spreading a large amount over 6 to 12 months is a common middle path.

For debt funds, yes. For equity, it depends on how you would feel if the market fell 20% the next month. If that would make you sell, park the money in a liquid fund and move it across in monthly instalments.

A quick way to estimate doubling time: divide 72 by the yearly return. At 8% money doubles in about nine years, at 12% in about six.