Poking around it looks to be 15g.
I'd poke around the forum a bit maybe to see what others think, but with my S I went sliders not rollers. Helped more than a little & I did kinda wish I'd gone a bit lighter like you're looking at; albeit the bike was liveable at stock with a slider where there was a huge flat spot with the stock rollers.
Springs? No clue, never did change 'em 'em out.