I have 3 mango seeds wrapped in damp paper towels in plastic bags in the windowsill, two of them are showing a little root on the end. When will it be ok for me to plant the mango seed in a pot? How big should I let the root get?

Once It is big enough to plant, how big of a pot should I use? What type of potting soil is the best? My aunt has soil from her compost, could I use that?

And one more question. If the mango seed does grow, how often should I transplant it into a bigger pot?