Quote from: pocrypto on October 09, 2018, 10:41:32 AM

I'm looking for a way to create and manage 1 million bitcoin addresses for 1 million of our users, any method is limitless and scalable. Open source methods and no full node load are preferred.

You don't need full node to generate Bitcoin address and there are plenty script on GitHub to do that.
About scalable, i guess you should find/create script which support multi-threading and written on lower (not low) level programming language such as C++.

Quote from: pocrypto on October 09, 2018, 10:41:32 AM

Also there are any APIs that are not limited.

Honestly, i don't have much idea, but https://www.blockcypher.com/ is popular. Alternatively, you could use https://bitcore.io/ client/full nodes which have efficient API.

Quote from: bitmover on October 09, 2018, 11:34:53 AM

I believe bitpay.com is the way to go. Easy and tested a lot already.

Don't forget that bitpay is hostile towards Bitcoin