If I filed in 2018 but owed federal (i.e. no refund) do I need to fill out the non-filer info w/IRS in order to rec. the stimulus?

If you need to file a 2019 tax return, do not use the non-filer form because it will prevent you from efiling your 2019 tax return. Go ahead and file 2019. If you don't need to file a 2019 return, you can use the non-filer form. 

https://www.irs.gov/coronavirus/economic-impact-payments

what do i do if i filed a non-filer return?  it was a mistake!

i plan to file 2019 taxes, will i be able to do both?

Since a tax return with 0 income has already been filed for you, you must now print and mail your actual 2019 tax return to get it accepted. If you try to efile your return, it will be rejected.