Mango seeds germinate best at 30C, in an aerated substrate mix: 50% vermiculite/50% peat is the best.
The top 3cm should be only vermiculite once you plant the seed. Pots must be deep 25cm and narrow, they have a tap root growing fast. Seedlings grow better in smaller a container rather than a big one. Keep the mango growing until the stem is 6-8mm, then you can graft the plant. My seedlings grow during the summer to this size only in 3 months, because of the tropical summers where temperatures reach 20C at night and 30-35C during the day. Very important is to throw the seed out once is brown.
More heat means more growth. Light is not so important at this stage, in fact they get burnt in direct sun.