Tweeter @benfromcanada has challenged me to deal with a blogpost of his. I'm only too happy to do so.
Full disclosure; I also asked bossmanham to take a swing at it if he has time, since I'm sure that his response, as a Molinist, will be quite different from my take, as a Calvinist. Diversity!
The post is entitled: Christianity's problem with free will
Let me begin by establishing that I don't hold to "free will" with no qualifications. It is my position that the Bible presents to us a God Who is Himself totally free and perfect. He does not change His plan, He does not change His mind, He does not improve on anything or learn anything, because He is perfect, omniscient, and omnipotent.
I can't say it a whole lot better than Ephesians chapter 1:
7In Him we have redemption through His blood, the forgiveness of our trespasses, according to the riches of His grace 8which He lavished on us. In all wisdom and insight 9He made known to us the mystery of His will, according to His kind intention which He purposed in Him 10with a view to an administration suitable to the fullness of the times, that is, the summing up of all things in Christ, things in the heavens and things on the earth. In Him 11also we have obtained an inheritance, having been predestined according to His purpose who works all things after the counsel of His will, 12to the end that we who were the first to hope in Christ would be to the praise of His glory. 13In Him, you also, after listening to the message of truth, the gospel of your salvation—having also believed, you were sealed in Him with the Holy Spirit of promise, 14who is given as a pledge of our inheritance, with a view to the redemption of God’s own possession, to the praise of His glory.
Notice that it is because of grace, unmerited favor from God. We humans are wretched and rebellious against God. We can't dig our way out of our problem by good works, for one thing because none of us care enough about doing so. Thus Jesus and His sacrifice, and thus it says in John 6:44“No one can come to Me unless the Father who sent Me draws him; and I will raise him up on the last day. 45“It is written in the prophets, ‘AND THEY SHALL ALL BE TAUGHT OF GOD.’ Everyone who has heard and learned from the Father, comes to Me."
Everyone who who listened to and learned from the Father comes to Jesus, and v44 says that all who come are raised up. Straight progression, and it is the outworking of our sinful nature, how we don't care to come to God. So God transforms us, draws us, gives us a heart to love Him so that we afterward freely choose Him. Before, we freely chose sin and death; now we choose life and Jesus.
It's not "libertarian free will", not unfettered and not uninfluenced. I know it can seem that way to us, but the Bible tells us far more and far deeper information than our own limited vision and introspection can give, because it is the expression of God, Who knows you far better than you know yourself.
Notice, v11 that we have been predestined for an inheritance - to receive Jesus' great gift of Himself and eternal life.
v11 - He works ALL THINGS after the counsel of His will. He is free and unfettered to create and work out a perfect plan. We are influenced and fettered by stronger powers than we - sin and death from birth until Jesus saves us, and slavery to Jesus and righteousness afterward.
v12 - to a specific end, for God's glory.
v13 - Christians are sealed with the Holy Spirit. That seal can not be removed.
One more thing:
Romans 8:6For the mind set on the flesh is death, but the mind set on the Spirit is life and peace, 7because the mind set on the flesh is hostile toward God; for it does not subject itself to the law of God, for it is not even able to do so, 8and those who are in the flesh cannot please God.
The non-Christian can not please God, and doesn't care to. His mind is in slavery to death.
The Christian's mind is in slavery to Jesus and to life. Neither of these are totally free, and that's OK. God knows what He's doing.
So, with that biblical framework in mind, we turn to your questions:
1: How do you reconcile your belief in free will with your belief that god has a plan for us all?
Answer: I don't believe in free will, so there you go. Ask someone who does. :-)
2: Is free will a good thing or a bad thing? If it's good, why does god not allow it in heaven? If it's bad, why does god allow it at all?
Let me answer the question as corresponds to the proper biblical understanding: Will is neither good nor bad; it can be used for good or for ill and it depends on whether the person in question is under the control of death and sin or of Jesus.
Our wills are somewhat free, however, and yet my answer remains the same. Rick Warren has said "the greatest gift God gave us is free will", and that is idiocy. The greatest gift God gave us is Jesus, and Jesus has saved us from the necessary outcomes of our wills' bad choices.
God allows free will in Heaven because He has given us new hearts and new natures that always desire Him. In this life we continue to struggle with the flesh and temptation (see Romans 7), but in Heaven those will not be present.
Your third sub-question is the entire problem of evil summarised. I recommend you see this article.
3: If you can't adequately solve the previous problems, how do you solve the Riddle of Epicurus?
I can solve them, but I'll also tackle this lame dilemma so there can remain no question.
Is God willing to prevent evil, but not able? Then he is not omnipotent.
--He is able.
Is he able, but not willing? Then he is malevolent.
--Unless He has a perfect plan that includes the pouring out of His grace on sinners to redeem them, and also pouring out His perfect wrath and justice on other sinners, to show the justice of His righteousness.
This question assumes that humans are neutral or even good, and that's just not the case. Humans are wicked and sinful.
Is he both able and willing? Then whence cometh evil?
Is he neither able nor willing? Then why call him God?
--Good question; ask a Mormon.