PVC doesn’t really work well for a mast above 20 feet or so. Pipe couplers are not strong enough to join the sections, there needs to be a foot or more of overlap.

APRS uses packet radio to send position reports or send short messages. DRM is used for digital shortwave broadcast radio. The DRM encoding is used in ham radio for sending digital SSTV pictures with software like QSSTV and Easypal.

There is also the QMX transceiver from QRP Labs. It can do CW as well as single carrier FSK digital modes.

I would suggest getting a radio that can do SSB. There are a lot of digital modes that won’t work with radios like the QDX or QMX.

For higher voltages, you could build a Pierce oscillator from discrete components instead of using a hex inverter.