Is it permissible to unlawfully take the money of a disbeliever, such as by falsifying accounts or overcharging, and is one excused from going to the mosque to perform Dhuhr, Asr, and Maghrib prayers due to being busy working in an internet cafe?

It is forbidden to transgress against the property of a non-belligerent disbeliever. Therefore, deceiving him and defrauding him in accounts is Islamically forbidden. As for raising the price of an item in a bargaining sale, there is no objection to it as long as it is by mutual consent and without lying or deception. Your work in the cafe does not justify you abandoning congregational prayer, as it is obligatory.