The bitcoin p2p protocol does not directly permit transaction lookups this way. Maybe some bloom filtering would minimize the footprint, but it's still relatively complex to implement.

Electrum servers are maybe the next best thing - they do support the lookups you want, but they're less decentralized, and if your application is doing naughty things they could collude and manipulate only your results.

The bitcoin p2p protocol does not directly permit transaction lookups this way. Maybe some bloom filtering would minimize the footprint, but it's still relatively complex to implement.

Electrum servers are maybe the next best thing - they do support the lookups you want, but they're less decentralized, and if your application is doing naughty things they could collude and manipulate only your results.

How do I get my block or headers response to only contain 1 inv item instead of 500/5000

I don't think you can limit the headers results (you have to know all the headers to do so) But once you have the header chain, you can send a block locator with start:HASH(n) end:HASH(n+1) and you can download a single block.

Re bloom filtering, if you find nodes with the BLOOM_SERVICE bit you can tell them your filter, and the block data only contains your txs and the false positives allowed by your filter.