I've recently been learning Morse code and I came back to thinking about my project. I currently have a receiver, and adding a CW transmitter would be dead easy, for example the IRF511 circuit on Switching-FET RF Amplifiers page. DDS output at one end and an LPF at the other and I likely have a CW transmitter with about 5W output.

Now, if I give the microcontroller full access to controlling the hardware, it could take care of the T/R switching, offset frequency and side tone (PWM output). This opens up the possibility of having a full keyer in the Arduino.

The only negative here is that the receiver is DSB, which means I will hear CW signals on the opposite sideband unless I start looking at phased SSB or an IF with filtering. But there is nothing stopping me from upgrading later to do that, and a phasing SSB receiver could also be fed directly into IQ inputs for an SDR.