Greetings in the name of the Lord Thomas....thats the name I chose upon my reception into Orthodoxy!
I'm fairly new to this board as well. So from one newbie to another...welcome!
I definitely was not a 'cradle baptist' but just before discovering Orthodoxy I was about to begin attending the local baptist church. So I know where you are coming from with these questions.
I'll try to give some answers...and I hope they will be useful to you.
First and foremost, we do NOT pray 'to' the saints or Mary. However, we DO ask the saints and Mary to pray for us. I'm sure you've asked others to pray for you at some time in your life. This is EXACTLY what we do with the saints and Mary. We ask them to pray FOR us. When they pray they are praying to God, just like when your friends, or your pastor, or your wife would pray to God for you.
There is no difference here. Well, with the exception that those who have gone to Heaven, are are in the very presence of God, truly KNOW how to pray! They know how to pray alot better than we do. I reckon this has already been explained to you though, so forgive me.
As for Biblical evidence...well there's actually quite a lot. A few verses are as follows:
St James wrote that we are to "pray for one another..." -James 5:16
Paul wrote, "therefore I exhort first of all that supplications, prayers, INTERCESSIONS and giving of thanks be made for ALL men." 1st Timothy 2:!
In almost every letter Paul wrote he asked for prayers, and mentioned that he was praying for everyone in the Church.
Orthodoxy would say that when people go to Heaven they are not "dead" but are actually MORE alive than we are here on earth. So since they are NOT dead, but rather very much alive (though temorarily seperated from their bodies) they are still considered as much a part of the Church, if not more so than we are. For us Orthodox, we see those in heaven and on earth as being literally ONE family whether we're on earth, or in heaven. (see Ephesians 3:15)
This teaching can be supported by a bunch of Scriptural passages. A couple would be when Jesus told the Pharisees that "God is not the God of the dead but of the LIVING." Matthew 22:31-32 He said this in response to their saying people who had died were actually "dead" and either wouldn't live again until the Resurrection or for the Saduccees, who rejected the Resurrection would never live again. Jesus shot down their argument by saying they were already alive Resurrection Day or no Resurrection Day.
Jesus also told the Pharisees in John 8:56 that even though Abraham had been 'dead' for 1000's of years, Abraham actualy "saw" Jesus's coming into the world and was glad about it. Another verse where Jesus shows those in heaven are aware of what happens on earth is this:
Jesus said, "I say to you that likewise there will be more joy in heaven over one sinner who repents than over 99 just persons who need no repentance." Luke 15:7
The best evidence is actually from Revelation 4, 5, 6 and chapter 8. In these chapters we see a picture of the worship that takes place in heaven. In it are shown a picture of angels and saints taking prayers before God. Also in chapter 6 we see that the martyred saints are aware of the things that are taking place upon the earth. Throughout Revelation actually, St. John says that "i saw" followed by things he saw taking place upon the earth. And in fact all the heavenly hosts see these events take place.
So the idea that those in heaven see and know what is happening on earth is supported by many Bible passageses. another would be the illiustration of the rich man and Lazarus. Anyways, since those who have gone to heaven know what is happening on earth, and since they are still members of the Church, and we're all one family, then the saints who truly know how to pray, will do so in heaven.
Thats some Biblical support for the practice...as for historical...I'm afraid I dont have references that I can post. I mean I have references, just not online...but yes the saints before 325AD wrote about the practice of asking the saints in heaven to pray for those still on earth. But again, I dont have them able to post...sorry!
As for Icons...well the use of Icons dates back historically to at least the early 2nd Century. As the catacombs in Rome, where the Christians in Rome would hide from the persecutions, have Icons painted all over the catacomb walls. If I recall, one of these Icons is actually an image of a woman asking a saint in heaven to pray for her. (I once say a picture of it, and that is the conclusion that I drew from it) Again, sorry I dont have references though. But these things are common knowlegde among Orthodox, so I dont think I'll get blasted for not posting a refernece.
One thing you could think of is that IF Icons developed later, like in the 4th century, why didn't ANYONE reject this 'new' practice? The Christians of that time fought dozens of heresies far more dangerous than this. Certainly if something so easy to prove as "new" entered the Church, someone would have said something about it. But no one did. (well in the 7th century an Emperor declared them wrong because of the influence of Islam, but the Church fiercly proclaimed that it was the Emperor's idea that was the "new" teaching...not the other way around. And again, this was all due to the rise of Islam. In fact the Emperor never said Icons weren't from Apostolic origins, he simply said since Islam so strongly rejected images (because they do not believe in the Incarnation of Christ) the Church should abolish Icons to appease Islam. The Church absolutely rejected this, declaring Icons had always been used, and were essential because they supported and declared that God became enfleshed in a material human body. (but thats all theological)
Oh in case you're wondering the 10 Commandments do NOT forbid the use of all images from being made. 3 chapters after God gave Moses the 10 Commandments, God COMMANDED Moses and the Hebrew to make images of angels, and other heavenly things in the building of the tabernacle and the ark of the Covenant. So even in the old Testament, images were used. When Solomon built the temple, it was arrayed in images. So the Bible doesn't teach images are sinful...just in case you thought it did, because that is what I was always taught. Until I read that God told Moses to make images that is..
I hope this is coherent Thomas..and I hope it isn't too much at once. If it is I apologize. Just take it a ittle at a time. Ask God to guide you. (as its obvious you already are doing) And if I haven't been clear, I'll be happy to try and answer again.
Your brother in Christ, Thomas