Now that my gamepad problems are sorted out, I can report a bit more on Recalbox usage.
Everything worked fine in the few included games (homebrews ?) I tested. The gamepad also works in Kodi, as does my TV remote through HDMI-CEC.
The only crashes I witnessed were in Kodi, and they were rare. I play movies from the network (via smb). They are stored on a NAS, with both the NAS and the Pi 3B+ connected to my router via ethernet. All the movies play fine, even those in 1080p, despite being read from the network. On one or two occasions, Kodi crashed and returned to EmulationStation. It seemed to happen exclusively when I tried to load a movie while another was already playing, as if Kodi/the Pi/the network (not sure which one of those) struggled. So now I prefer stopping the currently playing movie before trying to load another one.
Hope it helps.