SFBO Hybrd

I'm not very familiar with the hybrid voice scenario, but I can answer these questions in the context of using Skype for Business Online with Phone System in a non-hybrid configuration.

By Enhanced 9-1-1 I'm assuming you are referring to the service that transmits the caller's address to the 911 dispatcher. Skype for Business Online does in fact require you to specify an emergency address for each PSTN number you assign.

Call Park is not available with SfBO. (However, it has recently been added to Microsoft Teams as documented https://docs.microsoft.com/en-us/microsoftteams/call-park-and-retrieve.)

Media bypass is not applicable as all PSTN calls go through Microsoft's servers. (If you are wondering about the hybrid scenario, that is documented https://docs.microsoft.com/en-us/skypeforbusiness/skype-for-business-hybrid-solutions/plan-your-phone-system-cloud-pbx-solution/plan-for-media-bypass-in-cloud-connector-edition.)

https://docs.microsoft.com/en-us/microsoftteams/audio-conferencing-in-office-365. (Depending on which Office 365 plan your users have, it may require purchasing the Audio Conferencing add-on license for your meeting organizers.)