There are no limits or best practices for the TON API in terms of bandwidth. Instead, we limit based on chunk size and the number of requests you’re allowed to make during a given time period.
As noted in the docs, the maximum chunk size allowed is 64MB. However, we do recommend using a smaller chunk size like 32MB or 8MB as a safe default to help avoid timeouts during the chunk upload due to network latency.
For default TON API access levels, you’re limited to 50 requests / per user token / per 15 mins. If you have elevated TON API access you can make up to 90,000 requests / per user token / per 15 mins.