Hi Holly and welcome to the site. There's nothing wrong with combining a thumbpick with fingernails. I'm not sure if you'd get the "bluegrass" tone or the volume that way on a banjo though, but with guitar that would be fine. Many classical guitarists grow their picking hand nails long on purpose and keep them perfectly manicured to achieve proper technique and tone. Seems kinda sissified to me but whatever works I suppose. They look like they forgot to cut their fingernails on one hand I shouldn't make fun, classical guitar is amazingly hard and I respect what they do. I've tried it and it takes great patience and can be very frustating, for me anyway.
What was the question again? Oh yeah, the acrylic nails. I believe if it works for you and you're getting good tone and technique then keep doing it. But at the same time, it's always good to try new things and when you do, give it a good chance even if it doesn't feel comfortable at first.
I'm kind of a stickler on tone. I'm constantly trying different things to get good tone and believe it or not good tone comes more from technique, types and thickness of picks, pick angle, bevels, where you strike the strings and the attack than the instrument itself.
Since you got your guitar out, you may want to give flatpicking a try. You'll have a blast and Ben has alot of great lessons on flatpicking at all levels.
Hope this helps, J.W.