Is my sermon preparation routine adequate?

I think it is entirely adequate. I might switch the final 2. Although I understand the logic of doing it your way.

 

-You are definitely hitting all the bases. You mention prayer...this is the most important source for sermon preparation...continue there at every stage.
-You are also correct to consult commentaries late in your preparation; this does not, however, have to be after you have finished a draft of your sermon. The point here, as you are well aware, is that you want the message to be God speaking through you. One never wants to interfere with God's desire to do this by re-preaching the ideas of a commentator. Let God speak through you.
-It is definitely helpful to consult factual sources early. Dictionaries, handbooks, an Atlas, etc.
- Like Tom, I would flip your last two steps. I would know where I would take the sermon (w/o actually typing it out), but them I would consult some respected scholars and preachers in order to see what they had to say. At that point, I would prayerfully put everything together, write-out an outline, and prayerfully preach it through prior to the appointed time.

God bless you as you continue to grow in your ministry. If you are willing to put this kind of time into sermon prep, I trust that the Lord will bless your work. The saddest thing that we see in the ministry are ministers who take to the pulpit unwilling to put in any time at all. Keep serving Him faithfully brother.

 

That is a good routine. I like how text-centered you are in your preparations. I am sure while you are reading and re-reading the text you are identifying the main idea of the text and identifying the arguments and supporting material as the author intended it. A truly expositional sermon will be concerned mostly with explaining and conveying the message of the text, making application as appropriate.

There are some excellent tools out there that you might find helpful. One very good one is Logos Bible Software. Many excellent books on preaching have appeared of late that would be helpful too.