or just run a full node with the txindex option activated? That way you can use a simple json-rpc to query as much as you'd like without anybody limiting you... It's your node, your mempool, your txindex,.... the only one stopping you is you
Bitcoin Core JSON-RPC is limited, especially because there's no index for transaction.--snip--
txindex=1 is a valid bitcoin core option (default=0). When set to 1, a full transaction index should be maintained. Truth be told, I haven't run a node with txindex=1 for many, many years... Turning this option on requires more resources, and turning it on on an existing node triggers a full rescan..... But when turned on, a full node is sufficient, and json-rpc query's should do the trick... With this option, he should be able to query as many confirmed AND unconfirmed transactions as his hardware can handle.
For other things, like addressindex, you'll require a patched bitcoin core node, since such an index is not available in the default implementation... Bitcore used to have a patch, but afaik, they stopped using a patched node implementation around version 0.16.0 and switched to their own implementation (at least, that's what my memory is telling me)
--snip--
Unfortunately, I don't think they are ordered by the time received nor do I know of any API which does that.
the getrawmempool json-rpc query should (amongst other things) return the time:
"time" : xxx, (numeric) local time transaction entered pool in seconds since 1 Jan 1970 GMT