What is the most life you can have at the end of your first turn with only three cards?
With just 2 cards, you can be at arbitrarily many life points.
The 2-card combo is Black Lotus and Game of Chaos. As long as both you and your opponent keep playing, the stakes increase indefinitely, and you can end the game whenever you win a flip.
Assuming both you and your opponent keep playing exactly until someone gets to zero life or below during Game of Chaos' resolution, you can go to 103 life with the 2 card combo, or 109 with 3 cards.
If you win (+1), lose (-2), lose (-4), win (+8), lose (-16), win (+32), win (+64), then you (and your opponent) will be at

21 (19),
19 (21),
15 (25),
23 (17),
7 (33),
39 (1),
103 (-63) life.

At the start of the game, reveal Providence for another 6 life - this doesn't change the sequence of coinflips because your opponent would still fall to 1 life at the same point of the sequence.