Will the 4G sim card give internet access to other devices?

A 4G SIM card will not provide internet access to external devices like AC-coupled solar inverters; it will only supply internet to the SkyBox internally.

Should you need internet connectivity for additional devices, consider acquiring a 4G Wi-Fi router as suggested below. Inserting the SIM card into this router will establish a Wi-Fi network, allowing you to connect the SkyBox and other devices.

https://www.officeworks.com.au/shop/officeworks/p/tp-link-ac750-wireless-dual-band-4g-lte-router-mr200-tparchr200

Note: Skyenergy do not supply external modems and routers.