Does anyone here know some good references for designing with HBTs? Specially touching emitter sizing and biasing techniques for RF circuits.

Silicon Heterostructure Handbook by John Cressler, you have some applications there.

Thank you so much @Krzysztof Herman!

All writings of Barry Gilbert are a good read regarding BJTs in general.

[book] M. Schröter and A. Chakravorty, “Compact hierarchical modeling of bipolar transistors with HICUM”, World Scientific, Singapore, ISBN 978-981-4273-21-3, 2010, (World Scientific); refers to the application of bipolar transistors, which include the SiGe:C HBTs contact also https://semimod.de/services/