Please elaborate more how is the "1BTC liquidity" related to LUD-14's balanceCheck.

Wonderful! Just please use some rate-limiting.

One can get many new invoices without paying them by just opening https://satoshis.lol/.well-known/lnurlp/joel?amount=5000

This would be a possible Denial of Service vector. For example it may cause your LN node back-end to use too much memory for all those unpaid invoices until it stops responding to new invoice requests.