1)
I don't know the context, but isn't the subject "you" or "we", since it's 下手から行きすぎだ, not 下手から行きすぎた?
As you know, ~すぎ expresses "excess". It's usually about degree (too humble/modest), but also can be applied to frequency. For instance, こちらから行きすぎる only means "too frequently from our side" since "degree of from our side" can't be measured (and therefere doesn't make sense).
2) a)
That's わかって(い)て、やって(い)る "you know that, nevertheless you are doing it", not ~てやる "to give a favor of doing".
b)
Yes for "ことだろ doesn't come from that ことだ which is used to offer advice".
3)
として settles a hypothesis/plan to do.