Thanks for reaching out, I'm very excited. I figured I'd just drop a few thoughts from the top of my head to help you get started.
Bitcoin is the native currency of the internet. This community helps users that run into issues using Bitcoin, engineers building software that interacts with the Bitcoin network, and researchers learning about the involved protocols. Occasionally, business-related, economic, or game-theoretic topics will come up, but questions about the current exchange rate or speculation are off-topic. Other cryptocurrencies are not on-topic. Regarding the mood, I think we would like to emphasize that we are a technical community.
The most important symbol would be the Bitcoin logo: a slanted white ₿ on Bitcoin Orange. You may find the Bitcoin Design Guide (especially the Visual Language section) interesting. Our color is "Bitcoin Orange": #F7931A. There is a UTF-8 character for Bitcoin meanwhile, ₿ (U+20BF). As the Lightning NetworkLightning Network (lightning-network) is one of the most importantimportant protocols in the context of Bitcoin, lightning related themes may also be pertinent.