thank you for your interest in PyWPS and GSoC. Please use the PyWPS mailing list for further discussion of your ideas: http://pywps.org/community/.
Regarding your questions:
Do I have to get familiar with the whole PyWPS codebase?
It depends on the topic. For the implementation of wps 2.0.0 you will need more knowledge of the codebase than for "publishing data with help of QGIS MapServer". But if you already be familiar with Python, it should not be an issue to get into the codebase.
Must I have any geospatial knowledge to start?
Geospatial knowledge is always a benefit, but again this depends on the topic as well. For remote output storage there is less geospatial knowledge necessary than for publishing data with MapServer or Geoserver.
Are there any levels of complexity for these ideas?
We have drafted only the rough idea. In your application you should further develop this idea to show an implementation plan. The level of complexity is than based on your existing knowledge (= what you can achieve).
Can anyone, please, guide me regarding where should I start with?
Please subscribe to the PyWPS mailing list mentioned above and send your questions regarding the ideas you would like to work with.