Sean,
I don't see any mention in scripture that we should wait for the Lord's instruction on each action we would take. Maybe some people have done this and it has seemed successful but such would be the exception.
In the situation of a bigger house, I think we can too often get excited about the idea and give it our own approval. But its possible in this situation that God actually answered through the circumstances. It would have been a less certain answer drawn out by many offers with long wait times.
On the other hand if it truly were God's directive, then wouldn't it call for you to do everything you can to sell the house? Sometimes the real situations can be paradoxical -- acting against the troubles encountered.
I'm going to rely a bit on the NASB translation of Eph 5:8,10
walk as children of light ...trying to learn what is pleasing to the Lord.
I think we are usually to live a pretty normal life (going to school, working, buying homes, making decisions) while seeking also to live upon godly principles( showing love for one another, making sacrifices of comforts for others --give a way one shirt cause you realize God may have given that second shirt for a different reason than you first suspected).
So we may take certain actions and find out, by the consequences, that the actions weren't proper. This is the learning process. There's some wisdom also in seeking counsel, as Danny mentions, but even then the counsel can be off. If the counsel is someone older that you trust who shares wisdom on something like a bigger house, that then has more weight. The main element here is to grow in wisdom and grow in the knowledge of God through trial and error.
Abraham learned something when he tried to fulfill God's promise by having the child Ishmael. God was probably letting Abraham grow and make mistakes.
Now if God always answered prayer and it proved to be the wisest answer. The proven success of each believer would then move us from a reliance in faith into a reliance on simple fact and evidence. Right now we are really supposed to live by faith -- certainty-based knowledge is reserved for the future.
Why would God lead us to a dead end? If it wasn't God leading us then how are we suppose to ever know for sure who is leading us? Do we just make up our own mind? If so then why ask God if He's not going to respond?
I think we generally see God's leading from a retrospective situation, e.g. Abraham having the child through Sarah's servant. We have faith that God is leading us. Our prayers also show that we are remembering God and looking at our actions in light of Him -- that we are sharing our hearts with Him.
So I would say that yes you do have to make up your own mind. But do it prayerfully (which also reduces our actions under presumptions). If your action fails, you may see "the answer" as coming in connection with your prayers. If you didn't pray, then there was no reason (or less reason) to think that God was working behind the scenes.
The decisions are in your hands -- at least the decisions to move in this or that direction. Sometimes God may stop you from making a bad decision. But a lot of our faith is in God, that He knows what He is doing in our lives.
This topic is generating more ideas than is practical to write right now.
Blessings,
Mike
