No, but you are concerned about scalability while I don't know what you are doing, that is the key word that I would use a 3rd party api. Lowest overhead and easiest to be scaling with.
"Scalability" is ultimately limited by the Bitcoin network, which-- by definition-- a Bitcoin full node can handle. Interposing a 3rd party does not necessarily improve scalability-- it likely reduces it, especially since you're talking about unpaid services, so there is nothing to fund your utilization-- and using a third party service necessarily reduces security, more so than SPV, and necessarily adds additional points of failure: the reliability of third party blockchain services has been very low.
I'm sad to see that no one seems to have noticed the Baron link I gave above. It's a full order processing solution based on a local full node. It deserves more attention.