Thingspeak as a Data Source

Please excuse my naivety. I have very many (~10) sensors of my own design using ESP8266, which have been posting 8 fields of numerical data quite happily to thingspeak.com for several years. Whilst there is no specific problem with that, I am aware you can extract the time series data from them using a json query. Can someone please point me towards a working example using thingspeak, telegraf, influxdb and grafana where the data source is a thingspeak json request and the data is then stored any analysed locally (to me) for example on a raspberry pi.
I would prefer to do that, but I realise I could rewrite all the sensors applications to post more directly but I would prefer not to. Thanks in advance.