Also you mentioned you are working on a current starved ring oscillator, I have done a bit of work on that type of circuit recently, here is the repo in case you would like to have a look, in case it can contain anything that you may find useful or relevant for your work.
https://github.com/powergainer/vco I have testbenches setup for that and in that project I also had to go through the process of finding out how to do some basic analog things in the open source framework. One limitation I found was the lack of support of pnoise from ngspice. Another thing that I found useful in terms of open source EDA tools for analog design was this waveform viewer:
http://www.analogflavor.com/en/bespice/bespice-wave/ If there is anything I can help you with, I would be happy to assist. All the best