Is it permissible to combine Salat al-Ishraq and Salat al-Duha on the same day, each at its designated time, or must one be limited to only one of them, and what is the number of rak'ahs for each?

It is permissible to perform the Ishraq and Duha prayers on the same day. The Ishraq prayer consists of two rak'ahs at sunrise (the beginning of the Duha time), and some scholars consider it a part of the Duha prayer. The minimum for the Duha prayer is two rak'ahs, and the maximum is eight.