1. Ecowitt sensor arrays are all solar powered and have battery backup; their inbuilt solar panels are quite efficient - see
https://www.wxforum.net/index.php?topic=40730.0 for an overview of available and compatible sensors (and a lot of other related information) - for sensor details, look up
www.ecowitt.com - for extreme locations without sufficient sunlight exposure (e.g. Alpine valleys, polar regions) the batteries of the sensor arrays should hold 3-6 months
2. all other sensors are battery powered and battery life is usually between 1-2 years.
3. customizable consoles as you want them to be do not exist in the Ecowitt ecosystem,
however
- the webpage of your console shows only installed sensors (account at ecowitt.net needed) - as tiles, tables and graphs.
- to some extent the display of an Android app based console (on a tablet -->
https://www.wxforum.net/index.php?topic=39453.0) can be customized - all consoles can send their data to PWT via their custom server functionality
3. there are custmizable templates (webpages, you'll need a website for this, be in web hosted, be it on a personal NAS server) which can display your data on e.g. a tablet via the customized server functionality. (e.g. PWS Dashboard, Weather34)
4. if you want to start with temperature/humidity only, you could get yourself a GW1100 or GW2000 displayless console/gateway, a WH32 outdoor T/H sensor and 1-3 (up to
WH31 extra temperature sensors. Indoor T/H and air pressure will be provided by the consoles. The choice of these consoles will keep you open to a maximal extension of all available Ecowitt sensors, should you change your mind and want more in the future.
5. You can also at any time add e.g. a WN1980 or HP2551 console with display. The same sensors can be received, processed, displayed by many consoles in parallel. (Like a radio station and radio receivers).