I was wondering if I can use the Rx and Tx Hardware on the Arduino Uno and also add another Rx/Tx pins using SoftwareSerial at the same time ? cause I need two to communicate with two motor Controllers (Roboclaw controller) Thx
You can, but be aware that SoftwareSerial can cause problems if you need strict timing, as it will keep the Arduino stuck while it is receiving, as it polls in interrupt context.
I would recommend to check which one of the two serial channels is more likely to receive data and use the real HW Serial port for it.
The duration of the polling of the SoftwareSerial library is also influenced by the bitrate used on the port: the higher the bitrate, the shorter the duration of the lockups, so try to use the highest bitrate you can afford, on the Software Serial port.
In case you find out that you cannot afford letting SW handle one of the 2 serial ports, you can try the Arduino Mega 250, which has several UART HW blocks.
About the specific use case: if either of your motor controllers supports I2C or SPI, you could consider using that, as alternative to the SoftwareSerial.