The 'speksat' protocol is supported by all the major firmwares, I believe it was the first serial protocol used in multirotors. These days, the OSD is usually built into the FC and configured via the Betaflight GUI. This is not the case with the Femto FC that the gremlin power pack includes, you would need to use a camera as Psyborg suggests, or an addon board like a MinimOSD.
As for telemetry, the FC acts as a great many sensors when using FrSky or Crossfire, I'm not sure that functionality with Spektrum has been added to Betaflight yet, or if it can be.