Superthrive has only caused me problems in DWC and cloning. I would keep that little guy in a tray till some roots really started to show. Top feeding is fine early on as long as the stems aren't too long under the hydroton. Once the roots hits the water level you want, ditch the top feed. If it's too close to the stem, you could end up with problems.
Personally, I've found that making them stretch under floros when they are seedlings are best because I can bury them deep in the hydroton and just raise the water level to the bottom of the netpot until the roots drop out.