For an infrequent suit wearer a charcoal solid and a navy solid are all you really need. You can go anywhere at anytime, just add shirts and or ties and you'll always be appropriately dressed.
Now once you have these 2 basics you can add pinstripes in blue and grey.
I would not buy a linen suit for second suit.
I've heard there are 50 shades of grey, after the 4 basics I would focus here.