Yes, you are required by law to file a tax return because you have more than $400 of self-employment income. You *WILL* pay the self-employment tax on the amount over $400. But you will not pay any "regular" income tax.
Note that your disability pay from the veterans administration is not reportable on any tax return, ever. Additionally, even if only one of you had reportable income in 2018, you still file a joint return.
So the only thing you'll be paying is the 15.3% self-employment tax, and that's pretty much it. The SE tax is basically the employer's side of your social security and Medicare and gets credited directly to the SS account of the person who owns the business as will be identified by you on the SCH C.
