I am no expert on this so this could be wrong:
Probably but you will never exceed them. There are people here who automate factories and have no issues.
Not that I’m aware of. API calls are quite cpu intensive though. You’ll be cpu bound and tasks may get destroyed. Or MQTT message floods may lose messages if you overwhelm the network stack. Using mqtt QoS > 0 may help or may make it worse, as the messages are no longer “spray and pray” but have acknowledgements. However this will increase the amount of traffic possibly exacerbating the issue. Having said that mqtt is a really lightweight messaging protocol and you would be really hard pressed to actually cause this on a 100Mb/s link.
In short, for all practical purposes your answers are no, and no.