Well mainly, the effects will synergizes and you probably will feel squirmyfrom excess norepinephrine in your synapses. Ritalin is known for being dirty and causing a harsh cone down, why would you taint your amphetamines with it? It will probably ruin the amp euphoria and make the conedown that much worse. You will probably be fine and no long term damage will happen if you keep your dosages low, but the experience will be very dirty and you probably will feel anxious and over stimulated.
You seem pretty adament about trying the two, so go ahaeadx combine them. If you feel like shit then you know that it probably isn't the best idea.
Combining the two is more dangerous than just taking a higher dose of amphetamines because the effects will synergizes and possibly cause tachycardia or even serotonin syndrome. When you combine the two, its not like just adding more amps which would be like 1+1=2, but more like 1+1=4 , just like combing benzos and alcohol. I doubt you will have long lasting malacious implications if you combine the two, but do your body a favor and don't combine the two. The combo will put stress on your body and brain.
But fi you are like me, I didn't care about what people said and combined drugs. I found out the hard way thT combining drugs is very dangerous.