I am wondering if anyone know any good resources (books, etc) for management of websites

This is hard question to answer without a bit more knowledge about what type of website you going to be responsible for and what type of skills you already possess. From you post I am assuming you have working knowledge of html, and by virtue of posting this on PerlMonks that you have knowledge of perl :) However, there is no mention about your administrative experience at all. Are you looking for stuff on maintaining databases or webservers? Are you looking for books on how to design layouts or information architecture of websites?

The plan is to grow to several stores ( 2 < n < 50), and court a sale to a larger concern and get out.

This statement really concerns me. This makes it sound like growing a retail venture from 2 to 50 stores can happen overnight. To grow from 2 - 50 stores is something that is going to take a long time. So, in taking on this project you are looking at a potentially large time commitment. Maintaining a (e-commerce?) website for a business that large is probably not something that you want to do as a side job. There is a big difference in setting up a website for a friends at-home business and setting up something that is expected to grow into a chain of stores.

So, I guess the two major questions you have to ask yourself before you take this job is:

1) What skills do I need to learn before I feel comfortable stepping into this role?
2) Can I perform this role as a side job without losing my sanity.

Those two questions are pretty related :) Getting a small business of the ground is a LOT of work, so getting involved is potentially a serious commitment.

I'm sorry if this sounds like I'm being overly critical with my comments. This is not my intent at all. It just sounds like you might be jumping into something much bigger than you can handle, and because this is a friend's venture can make it trickier to get out if things go wrong.