I have put the boards in a rather large case in order to provide enough room inside the case for future experiments and added two leds, a green one for power on indication and a red one for TX indication. As digimodes are at 100% duty cycle and possibly overheat the board I calculated the space for two fans in case I have to cool the board during operations. For the PTT I decided to use two buttons, one pushbutton and a flipswitch. They are connected in parallel so I can decide if I want to keep the button pushed during transmission or just flip the switch and flip it back after the digital transmission finishes. In the future I might even look at an transistor switched PTT connected to an RS232 interface at the computer.
First testing revealed one major problem. JT9 and JT65 need the upper sideband to function properly and the BITX40 has natively only the lower sideband available. I have read about some mods which should enable the upper sideband as well, but did not have the time yet to try that. Although I was not able to test JT9, JT65 and WSPR, I was able to do some PSK31 and found out the the board does not heat up that much during transmission as I expected. There even might be no need for any fan at all!
Lets see where this little project is going and many thanks to DJ0GX for his reply on my CQ and the 589 RST.
73 de OE6AVD (Alex)