Hi!
First congratulations with getting sound out of the SID, it's always a huge moment 
Concerning your ghost notes issue, I had the same one with my own SW, which I eventually solved by adding a 300us wait command after each SID write (see the library, inside the SID.cpp). It seems, but I could not verify it firmly with other internet sources, that the SID somehow needs time to store Data, event if the transmission time is announced to be much faster in the datasheet. 300us is Ok for sound devices.
I'm curently in the process of building a MOS6581/8580 datasheet using feedback from my own work and scanned versions of the datasheet from SID websites. you can find it here, I added other tricks and tips that shall help (note: it's not finished and will be improved alongside with the SIDaster updates).
Concerning the SIDaster Shield & Synth, 5x5cm Shield prototype is almost finished, as you can see here. I'm still waiting for another development board I have designed to continue with SW programming. Next release will include Preset handling through Dedicated Sysex Messages, Polyphonic - 3 notes - mode, and first release VST Gui that handles patch editing and preset saving (Windows only). Preset format and Midi implementation is already detailed on the project page.
I don't want to commit on a date, but it's moving on. This is a spare time project and I'm quite busy with regular job stuff ATM.
Regards,