Q1- Did the Apostles have special understanding by the Holy Spirit afforded to them?
Yes, there are two passages in the Gospel of John specifically state that the Spirit would be manifest in the disciples in a way that cannot be duplicated in believers that followed them.
[Jesus speaking to the eleven disciples]
(1) But the Helper, the Holy Spirit, whom the Father will send in my name, he will teach you all things and bring to your remembrance all that I have said to you. John 14:26 (ESV 2016)
(2) “I still have many things to say to you, but you cannot bear them now.
When the Spirit of truth comes, he will guide you into all the truth, for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come. John 16:12–13 (ESV 2016)
Q2 - In regards on how to view and apply the OT prophecies concerning Jesus as coming Promised messiah?
Regarding the interpretation and use of OT passages relating to Jesus coming...
All Scripture is breathed out [inspired] by God and profitable for teaching, for reproof, for correction, and for training in righteousness, 2 Timothy 3:16 (ESV 2016)
Rob