Need help on animating materials

So basically I want to make this 2d animation of a flower sprouting and blossoming into a flower…I already have 10 images of different stages of growth of the plant and I tried making a flipbook and it was pretty good But it wasn’t exactly what I wanted…so here’s a brief overview of my idea:

When the animation reaches the 5th texture/image/frame I’d like the flower to glow(using emissive on the texture/material) and when it reaches the final development (10th texture) I want it to glow even more and displays a simple particle effect. Since it is a 2d image on a plane I want it also to always face the player ( I experimented with billboard, but I can’t seem to lock the axis I want )

Anyone might be able to help me on this?