Cant help with any of these apart from the first one.
The Sonic Fighter was a beginner level model in its day. 2WD and similarly designed to the Striker that preceded it. The Sonic Fighter had oil filled shocks up front.
For more info see here
http://www.tamiyabase.com/models/models.htm
In answer to your questions, yes i have one, yes they come up for sale on Ebay and arent particularly expensive
HTH