The tutorial uses Blender 2.79. With Blender 2.8 came a big update and some things may have changed or might no longer work as they did. There are still a few old known bugs in Blender 2.8 regarding particles and Dynamic Paint (such as update problems).
Let's start with the real problem first.
Problem 2 "Particles don't paint Dynamic Paint" - no longer supported in 2.8+
In your project, the text object is used as Canvas and Brush at the same time. This is no longer supported in Blender 2.8 and higher. See bug report T64149 -Regression in dynamic paint, blender 2.8: cannot make an object act as canvas and a brush simultaneously. Quote:
We do not support this in 2.8.
Having the object be both a canvas and a brush at the same time could lead to very bad dependency cycles. So not we made it so that an object can only be either or (as implied by the GUI in 2.79 and 2.8).
If you try this in Blender 2.8 then Dynamic Paint is just disabled and you only see the manually painted vertex paint (white by default).
- create a linked duplicate (Alt+D in Object mode) of the Text object. Then both objects share the same mesh data so you don't have to worry they could be different.
- make one object a Canvas and remove the Brush in the Dynamic Paint settings. Also, remove the Particle System from it.
- make the other one a Brush, remove the Canvas and keep the particles.
- on the Particle Settings tab, in the section Render and Viewport Display hide the emitter object (the Text (Brush) object) by unchecking
[_] Show Emitter so it's not rendered twice (see 2nd screenshot below). Otherwise, you get shading issues and it covers & hides the canvas → big confusion!
- for the Text (Canvas) object you need to create the vertex groups dp_paintmap and dp_wetmap for the Dynamic Paint:
See Dynamic paint does not work on canvas in paint mode for details. By default, the section is collapsed and you don't see the red field that indicates the missing vertex groups (error).
If you want to see the Dynamic Paint for a burn effect or just to check if it's working you can use the Vertex Color node in the Shader Editor:
Problem 1 "Different Halo Size" - not a problem
Don't worry about the Halo size. The halos that you see in the viewport are just for visualization. This appearance is just used in the viewport, not for render. Halos are probably a leftover and not even rendered in Blender 2.8+.
You can change the appearance of the particles in the settings for the rendered image and for the Viewport Display individually.
If you want to have smaller or bigger halos in the viewport just change the Particle Properties > Viewport Display > Size value.
If you want to render the particles, set Particle Properties > Render > Render As to
Object and choose an object.