1 - the hybrid system will automatically select just ICE/EV assisted/EV only mode depending on many factors (battery state charge, how warm the cabin is, throttle position, engine load, engine/battery temperatures etc.) - just let it get on with it as in general it is selecting the best mode to use at that particular moment in time.
2 - by design it won't charge the battery passed 50% so there is always buffer to accept some charge from the regenerative brakes. If you want to get the battery full then coast down a very long hill/mountain road.
3 - You have the EV button which forces EV driver mode. This is really for moving the vehicle out of a garage or around a car park when you don't want the petrol engine to run. It isn't an efficient mode to be in so you should use it sparingly.
4 - The hybrid battery is very small (a maximum of 1 or 2 miles range, it isn't an EV). If you run in EV mode for too long the petrol engine has to fire up to recharge the battery when it gets low.