Its summer here in Sydney and its hot. Today was 32 degrees (C). The only things running on the farm are the Raspberry Pi's.
I got another 5 port USB charger. The ones I'm using to run the Pis are an Astrotek brand. Its a 5 port 8 amp unit. If you only plug 4 devices into it it can provide 2 amps per port. If you plug a 5th one in it drops the available power so I normally run four. The second charger is running the four Pi2's that have been sitting around gathering dust. I get a RAC (recent average credit) on Einstein BRP4 of about 300 from a Pi2's and 515 from a Pi3.
There are some rumours of a Pi4. There is nothing official at the moment but historically the Raspberry Pi foundation announce new models in February. The suggestion is it will have an ARM Cortex A53 processor at 1.8Ghz and 2Gb of memory. There are contrary suggestions that there won't be a new one for a few years as the foundation ordered 600,000 Pi3's and would need to sell these first.