Do the usual asthma and add meds for children interact with one another in any bad way?

Sometimes uncomforta. Stimulants and asthma inhalers may cause tremors, jitteriness, or anxiety in susceptible people. They may also increase blood pressure. Combining the drugs increases the probability.
Possibly. My direct experience is frankly limited; however; my sense is that both are similar as their adrenaline like effects. And yes there are allergic reactions of a serious nature plus we all are unique. Discuss this with your physician; please pick the one you are most comfortable with as the central physician, and proceed with all the collective knowledge and experience now at hand.
No. One of the many reasons we use inhaled medications for asthma is that it is easy to reach the target organs - the lungs. This way, we are able to use much lower doses, and tailor the medications and drug delivery so that there is little absorption of the drug to the rest of the body. Because of this, there are no meaningful interactions between inhaled asthma drugs and other medications.