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This sounds a little risky. I would avoid doing redirects if possible. If this was my site, I would get into my analytics and find out which 100 pages are pulling in most of the sales from people who enter from search.   I would then spend whatever time it takes to recode about five pages by hand,  using the best SEO practices within my ability. I want to make them into something kickass. After I did the first five of those pages, I would get in touch with a consultant, show her those pages (before and after shots), tell her the goal and have her give opinion on what might be done better.  When I do something big like this I always get second opinion from someone who does more SEO than me and who is smarter about it than I am.   I might ask a question on Moz or get a friend to look at something.   I always get advice from people I trust when doing this.  I don't worry about cost.   One taken opportunity can be worth literally a million dollars in the long term.  One screw up can cost many thousands of dollars immediately and millions over time. So, after these consults I would launch a few dozen hand-crafted pages and see what happens.  A couple weeks later I would launch  more if the results were good. The higher the value of these pages the more that I would do by hand.  Once I thought that I had things under control then I would write or have written a program to do the rest of the job automatically. I am never in a hurry on a high value job like this.