From bottom to top, from testnet to mainnet, every layer is available to access blockchain data: explorer, submit, graphql, ogmios, postgREST...
Check GimbaLabs site for info about endpoints and education content to get started on experimenting!
No worries, start by exploring our free APIs and think about hosting/scaling later, we might help with that also in the future by offering some paid plans!
Do you think your idea can help on growing Cardano's ecosystem? Then don't forget to participate on Catalyst project by submiting your idea on IdeaScale, get feedback, iterate on it and who knows, maybe, get DeCentra-funded!