The bottom of the booga bag is knit first, so if you want to add eyelash yarn you will want to do that at the end of your knitting. As for doing that specifically, I have never added non-felting yarn to a felted item so I can't help you there!! Someone else will, I'm sure.
And about the yarn, I have made a booga bag out of Patons Classic Wool and it came out just fine. What color are you going to do??
Have you ever knit 'in the round' before? This pattern is made on a circular needle, which sounds daunting at first, I know I was pretty nervous about it!! The booga bag was my first circular project and I found out that it was actually very easy and nothing to be afraid of.
Good luck and give a shout if you need more help!