I'm not a credo-baptist either (anymore), but the only "hard-and-fast rules" that were followed in the credo-baptist churches I was in were:

1. - That no one was baptized unless they could articulate their faith, confessing acceptance of Christ as Savior and professing conversion to the Christian religion, and

2. - That immersion was the only valid mode of baptism.

One of them had abandoned a rule which in which baptism - even after verbal confession of Christ and by immersion, was nevertheless invalid if not performed by a Southern Baptist minister. They called that, "alien immersion." I don't think that rule is followed anywhere anymore... at least I hope not!

Like you, I hold that both believer's baptism and covenant baptism are Biblical. I also believe the mode of baptism is not restricted to immersion only.

-Robin