So your plan is not bad. But do think about calling rather than signing up online and set a predetermined close date if budget is a problem. That way you know there won't be any surprises if you forget to stop their auto renewals.
As I said in another message, I barely use any of the other people's trees unless I am at a dead end. Mostly I am collecting documentation, which is what Ancestry is terrific for.
For old genealogies, check Google Books and Archive.org - both have a lot of those old one published in the 1800s that you can download for free in various formats. I remember my Mom trying to find some of the titles back in the 1960s and not being able to get access to them. Now I can download the entire book and print the needed pages at my leisure.
I've got a big advantage over most people - my father's mother and her grandfather did a lot of family research over a hundred years ago. Then my mom researched her family fifty years ago. My husband's mother exhaustively research her lines and most of her husband's. But they did not have access to as much of the original information as I can now get online.
They could get census indices - I can get scans of the original pages, as just one example. Those old genealogies that were only in a few libraries are now online. Ship passenger lists that were not indexed are now easily searchable online.
My main pursuit is assembling more corroborating documentation rather than tracking down ancestors. I have been lucky to take some branches back further - Mom and Grandmother mostly stopped once they proved their Revolutionary ancestors for DAR. 
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