1) EOSIO Github: This is where you will find the entire public EOSIO code base, code to deploy a testnet, and other developer documentation.
2) EOS Developer's Blog: Here you will find regular (usually each 1-2 months) updates from Dan Larimer, CTO of block.one.
3) EOS Roadmap: The overall roadmap is published in the link below, however, please review Thomas Cox's update here.
4) Developer Wiki:
5) EOSIO How To videos
6) Videos explaining BFT dPoS, Resource Allocation, and General Q&A.
7) Basic to Intermediate C/C++