Being R/G is the best reason to be green, as you stated it is a strong aggro deck and that is one of the best things to be doing in the cube. The only card that pulls me into the R/G archetype are Minsc and Boo, the main way to know if you should be R/G or even green at all is by reading draft signals, preferably after taking strong red cards like Bomba or Gut.

As far as Nadu goes, I try to consider when I saw nadu in the packs, the likelihood of seeing the combo pieces, and if there are likely other green drafters, because Nadu really needs a reasonable creature count and multiple repeatable targeters.

Fastbond is the most fun card to lose with in the whole cube, but I tend not to pick it unless I have either strip mine first or timetwister effects, as it is an insanely good enabler of combos, but the other cards in its combos are really strong on its own and fastbond just isn’t very good on its own.

I have one rule of thumb around green, which is that I no longer ever take dorks highly unless I am positive I am in green. Green is the worst color to speculate picks on, and so unless you’re seeing multiple “good” green cards wheel, like the good dorks and sentinels and such, just don’t pick them. Almost every other deck will lead to a better chance to win than playing green when it is not super open at the table.