You are proposing to use mobile data for network access. Is that the only option available to you? If you have any way to provide direct internet access or, even better' link to the remote machine directly, you should get better and more consistent network performance.
Is 40 Kbps the peak or average data rate? You need to ensure that the output network speed is at least as high as the input data rate, and if it is then the need for local buffering should be minimal. But if your data rate is such that the output could be swamped for short or long periods, then this makes the design more complicated.