Creating a "Partial" Node

I'd like to have a "partial client" that participates in the Ethereum network but, unlike a full node, it only synchronizes state for a particular smart contract. The intent would be to detect bridging requests within that contract, to trigger more work related to bridging, but without depending on (1) a 3rd party like Infura or Alchemy to detect/forward events or (2) hosting my own Ethereum full node (which is heavy-weight). Things I'd like to know:

1) Is devp2p (i.e. RLPx) the proper place to start exploring, for creating my own solution? Or is it better to start with Gossipsub?
2) Would it make more sense to start with a light client code like Nimbus or Prysm?
3) Are there key reasons / technical challenges that would make this effort daunting?