Icons are 24x24 size because that is the max that Street Pilot can take. I do not know what is max Honda Connect allow. Street Pilot can only play build in tones so it should make DingDing sound when alert is active. Again I do not know if Honda Connect allow .wav or .mp3 audio.
You need to test via simulation to know if
1. It's correctly using desire alerts (make sure you only have my .gpi's under POI directory)
2. It's working correctly (directional wise)
Alerts are searchable so I suggest you use that to make testing easier.
If you give me a test coord (lon,lat) I can build a test .gpi for you to try to see if larger icons and better audio can be used under Honda Connect.