My question is, how much would you use for a 3 mug of basmati rice? is 5g too little or too much?
Far too much, you only need half a dozen or so strands, a small pinch.
There's a number of different ways you can use saffron - as strands, ground or soaked in milk. You can add strands directly to your rice just before adding liquid, you can grind them in a pestle and mortar and just use the powder and add this before the liquid or soak them in a couple of tsp's of warm milk and sprinkle this over the rice at the end of cooking. I usually take my rice off the heat and let it rest for 15 minutes or so and it's at that point I would sprinkle the saffron milk over the rice, just as I take it off the heat and let it infuse for 15 minutes. This gives the rice a nice natural mottled yellow and white colouring.
I get my Saffron in Spain from the local market for 10 euro for 5g so, 6 euro for 5 grams from Schwartz is pretty good going. I'd check to make sure it is 5g, as I don't recall Schwartz doing 5g jars of Saffron, they're more like 2g.