(1) my concern that it was being declared as a sign gift that every believer must have as proof of being filled
It was never used as "proof." The proof of one being filled with the Spirit is clear - they are dead to sin, and have a new nature. But the Spirit we receive does also manifest Himself through His gifts. As far as tongues, there is the sign and then there is the gift. The sign reference is in Mark 16, whereas the gift reference is in 1 Corinthians 12. All who believe are given the sign gift whether or not they use it, or even know they have it, so it can not be "proof." It is part of the armor of God allowing us to pray God's perfect will. The gift is not given to all, and is only used during a church service. It is restricted to two or three and is
required to have interpretation. This is unlike the prayer and praise language that can actually be done altogether as the 120 did on the Day of Pentecost. Even though the devout Jews supernaturally understood their individual language among the cacophony of different languages spoken, interpretation is
not a requirement. Our prayer and praise language is what is called a "sign to the unbeliever" but that can easily be misinterpreted. It is the same type of sign as the sign of Jesus in Luke 2:34 - a sign which will be spoken
AGAINST. An unbeliever or an uninformed Christian will mock tongues, as the mockers did on the Day of Pentecost, and is recorded in answer to verse 22 in 1 Corinthians 14:23. Together these two verses should stop the misinterpretation that tongues is for the purpose of preaching to unbelievers, a total fallacy. That is not to say that God can't produce a miracle with regards to language barriers, as Oscar recalled in Italy. But, again, that is not the purpose of the sign gift.
(2) that people were interrupting the exercise of a different gift to get their message out.
Tongues is totally in our control. Anyone who disregards Paul's instructions to NOT interrupt another gift, is out of order.
(3) that “singing in the Spirit” seemed to me like an en masse disregard of the God mandate for interpretation.
When the 120 all spoke in tongues together on the Day of Pentecost, it could just as easily have been sung. Here again is the misunderstanding between the sign of tongues and the gift of tongues. What you are referring to regarding mandates is only for the gift. But in a service where all who are present are Spirit-filled informed believers, praising God in song as a choir is allowed.
(4) that a person would speak in tongues for maybe 10 seconds, then give a 2-minute interpretation.
Interpretation does not mean word for word translation, therefore can vary in length.
(5) a straight up prophesying would have sufficed
God commands us what to do, we don't tell Him what will suffice. It is called, the fear of the Lord, and that is the beginning of wisdom. So be careful not to fall into pride, that your reasoning is better than the Lord's. Just look at the way Jesus healed. He mixed it up, hardly ever healing the same way twice. That was on purpose to teach us His ways are not our ways.[/QUOTE]