1) The price increase is mainly due to including the microSD card. Also, since earlier this year, we’ve been using our local manufacturer (WAi) for the production of OS 2.3. It’s more expensive than Chinese manufacturer, but it’s now all made in the US.
2) OS 2.3 (AC) version has 3 analog pins and 3 digital pins free to use. The DC version has more pins (because it uses I2C LCD which frees up some digital pins). All the spare pins are mapped out to the upper left corner of the PCB. The I2C, UART, and SPI pins are also mapped out, so if you have sensors that use I2C, UART, or SPI, those can also work.
3) I am not familiar with Wind sensor and we don’t have current plan to add support for Wind sensor. For most simple sensors you can just follow how rain sensor is implemented.
4) We are working on adding support for flow sensor / meter in firmware 2.1.6.
6) Our current weather script does take into account of weather forecast of the day (although I don’t think it looks beyond 24 hours).