Wood
 

I am using poplar dowels for a top water plug for stripers is this a bad choice?

although you can make plug out of just about anything, poplar is difficult to seal, I've used it, so have alot of other builders... with mixed results... it tends to split eaisily if not sealed real well... cedar or bass wood , even clear pine are better choices for surface poppers/swimmers..

Ya gotta start somewhere. I think they'll be fine. Got a picture?

I'd use whatever I had to start. The first ones are all throwaways, well save the first one throw away the next 99. It's a great hobby and doesn't have to cost a fortune.
I'll give you a hint: the best poppers swim