The glue is needed mostly as a protective covering for your eyebrow hair. As most of us who paint know, acrylic paint is not very fun to get out of hair and clothing. I once accidentally got white acrylic paint in my hair and it wouldn't come out for 2 washes without ripping out hair :\. Not to mention it usually never comes out of clothing. I don't think any of us want to chance walking around with clumps of our eyebrow hair missing XD
Stiff eyebrows feel the same as putting a layer of gel over your eyebrows. It takes a few minutes to get used to, but its not as if you can't move your eyebrows at all.
When you say "thicker and bigger" I am assuming you mean something like Rock Lee's eyebrows from Naruto. In this case, I would try overlapping the glue further onto the skin around your eyebrow. Do 2 (or if needed 3) coats of the glue so you don't notice the hairs of your real eyebrow randomly within the painted one, and then try the paint.
Let me know how it turns out. I'd be happy to help more.
Also, for those who are intested, I'll probably be adding onto this tutorial closer to the summer months as my friend will be dressing as a character with very small eyebrows, so we'll need to cover up half of her eyebrows to look like skin. I hope it will help those who are asking about how the change the shape of your eyebrows a bit.