It seems to me that your actual problem is getting the balances for numerous Bitcoin addresses. As @darosior noted, the service you were looking into does not appear to offer an API. However, e.g. blockchair.com has an API endpoint that allows you to query up to 25,000 addresses at once. Even though blockchair.com also limits queries, you may be able to ...
Will this cause issues when running btc-rpc-explorer if I wanted to query old data?
Yes, as it requires txindex.
And if so what is the appropriate pruned node amount to access 1-2 years of blockchain history?
txindex is currently only supported without pruning, so you need to have a non-pruned bitcoind to use btc-rpc-explorer.