Every output of a transaction needs to be explicitly spent as an input eventually, but there is no need to stage deposits separately and resend them to yourself again. Maybe I'm missing something, but you could and should give out addresses of your service's wallet to your users and thus get deposits directly into your wallet. If you give each user a new ...
You may have received such small amounts that it is impossible to accumulate them in one transaction due to the restrictions on the size of the transaction.
Try sending 0.3 BTC and then 0.2 BTC in a second transaction (be prepared for unexpected large fees).
It is also worth analyze your UTXOs. Maybe you have such small amounts that they are flagged as ...
The blockchain.com link given in the accepted answer no longer works.
From the published API
The URL you need to download a HEX formatted block is as follows.
This gives you a hex formatted file that can be converted to binary with xxd -r -p as above.
The bitcoin block ...