Struts should be as stiff as you can get them depending on their diameter, super skinny needs more pressure.
9PSI seems to be a good useable number for most kites.
The gravity trick works good for the ball valves, but being quick with the hands makes any old valve work.
You can also pinch the valve down below the end while you insert the plug.
Once you pinch and shut them a few times its will seem easy. Or it does to me anyway.