Fairly easy to install using the install procedure here Running on Android : Node-RED
You need to install termux using fdroid not google store.
Here is a good install and start up readme. Android - termux - Playstore no longer a recommended install source - #5 by btsimonh
As to other questions yes to all. you will need to install termux api app, then you can send messages call phone number etc using the exec node.
You will need to learn about termux, there is a lot of information out there on the web though.
