Well it is best, quality-wise, to leave it at 48kHz. The question is whether you are willing to give up some amount of compatibility, since both VCDs and SVCDs require 44.1kHz audio. Most dvd players don't seem to have a problem with 48kHz audio in a VCD or SVCD. If you do resample then either keep doing it prior to importing to TMPGenc, or use an external frequency rate converter, like Shibatch encoder, as a plugin to TMPGenc. Many people have complained of TMPGenc's internal frequency rate converter.
As for bitrate, joint stereo is sometimes a better choice at lower bitrates. For a 2 channel audio track, 224kbps is more then enough to warrant using stereo over joint stereo. I personally wouldn't switch to joint stereo until my audio dropped below 192kbps.