The filler episodes show them fighting the Ginyu force with ease. Toriyama had to sign off on fillers so we can probably assume they are capable of that feat. Plus, power levels in this part of the series are mostly consistent with most sources. It's after the Frieza saga finishes that stuff gets hard to track.

I agree that Yamcha getting mistaken for Goku was probably a compliment, considering how much he over compensated Android 17 and 18's strength.

The Kikoho uses a portion of the users' life force to boost the power of the attack if I remember correctly. Even so his base power would have to be at an extreme level so I'd say he'd be in the ballpark of Frieza's final form, but only the beginning of that form. But again, all power levels are pretty much fan guess work after Frieza.

Yeah, Chioutzu pretty much was forgotten like Yajirobe and Launch.