Jesus speaking through the Holy Spirit [Acts 1:2] does not mean that the Holy Spirit spoke to them directly, but that Jesus spoke by the power of the Holy Spirit. The Prophets also spoke by the Spirit, as did Jesus to the imprisoned spirits
[1Pet 1:12; 3:18-19]. Preaching is by the Spirit of God
The calling of prophets is not to witness but to deliver a message from God, while the calling of the Apostles is to bear witness to Jesus [Acts 1:8]
The cloud did not “hide” Jesus as the NIV states, but it cloud took up/received (Hypolambano) Jesus from their sight [Acts 1:9]. It wasn’t some rain cloud or other earthly cloud that hid him.
One of the requirements for the replacement for Judas was that he must have been with Jesus since His baptism by John. This rules out Paul – who couldn’t have borne witness of the beginning of Jesus’ ministry.
The Apostles prayed that God choose as Judas’ replacement, one whose heart He had searched [Acts 1:23-26]. God chooses and gives His gifts to those whose hearts He has searched; as in the case with Simon who was rebuked by Peter for
seeking the Holy Spirit with an impure heart before God [Acts 8:17-24].
Acts 2
The Apostles were “sitting” when the Holy Spirit came upon them [Acts 2:2]. This helps guard against those who might say that there’s a position to take to receive God’s Spirit. Sitting, standing, lying down; it makes
no difference.