Negative power & Chandra's Pyreling

You are correct. From the complete rules:

107.1b Most of the time, the Magic game uses only positive numbers and zero. You can’t choose a negative number, deal negative damage, gain negative life, and so on. However, it’s possible for a game value, such as a creature’s power, to be less than zero. If a calculation or comparison needs to use a negative value, it does so. If a calculation that would determine the result of an effect yields a negative number, zero is used instead, unless that effect doubles or sets to a specific value a player’s life total or a creature’s power and/or toughness. Example: If a 3/4 creature gets -5/-0, it’s a -2/4 creature. It doesn’t assign damage in combat. Its total power and toughness is 2. Giving it +3/+0 would raise its power to 1.

So a negative power value is NOT treated as zero unless it's going to have a direct effect on the game like dealing damage. All other times (including your example), normal math is used, so 1 (initial power) minus 2 (so tiny) plus 4 ones (triggers) is 3.