Is there such a service as an unlimited Bitcoin wallet with an API? Well, I did tons of research and currently I'm using bitcoinlib for python to have a wallet which should be able to hold over one million addresses and occassionally broadcast transactions. 

It has all the features you'd expect, but I'm concerned about performance when I use more than my current 10 addresses. 

The thing is that I'm trying to make an online plattform which relies on the Bitcoin infrastructure and there could be millions of users. Also, I am concerned of how secure bitcoinlib actually is and I'm missing a neat Graphical User Interface.

Now, there are wallet services like Coinbase which also offer an API but I don't see any explanation on how many addresses they could hold or how many API requests I'm allowed to make. I've found many of those seemingly free services, so Coinbase just serves as an example.



Hence my question, is there any such thing as a free bitcoin wallet service (we're a free platform, so no budget there) which could scan let's say 100'000 addresses and notify our platform of incoming transactions within a few seconds and broadcast about 1000 transactions per minute ?
While I'm not sure of the technical requirements or limitations you have around building you platform. It sounds to me like your best option is simply running your own Bitcoin node itself. There are lots of online examples that could help you get started. I found bitcoin.org's guides particularly useful: 


https://bitcoin.org/en/developer-examples
https://bitcoin.org/en/developer-reference


This will also give you benefit of actually holding the keys to the funds on your platform as well.

For monitor transaction sent to your node's wallet, I'd check out the ListTransactions RPC call, and for broadcasting transactions, you can use SendToAddress, or CreateRawTransaction, SignRawTransactionWithWallet and SendRawTransaction.

I should also add that running your node can be almost free (just need a computer running the server), and that you do not need to actually mine BTC on the node (which consumes a lot of energy &amp; resources). Your node will just be monitoring the chain and broadcasting your transactions.