What other things does your Mega do beside controlling the AC as you could maybe just use the D1 and ditch the Mega altogether.
I use Dweet.io, Cayenne, ThingSpeak & ubidots. I also used to use freeboard.io but despite it's name it became non-free so I ditched it.
How much data are you talking about? I have 15 channels on Cayenne, 11 on ThingSpeak & 10 on ubidots. I publish data to them all every 15 minutes but Cayenne can accept data every 30 seconds (not sure about the rest).
Cayenne was my favourite as it had everything I needed but then it stopped working with Apple IOS9 (both the App and Safari) so I now route everything through dweet.io and use node-red to collect the data at work.
No need of a static IP as their are web services that you can get your WAN IP from (www.ipify.org to name but one) and then just publish it to something like dweet.io for your code to pickup. But it is always better if you can avoid having an outside route to your internal network for security.