I have used consultants for Perl project with the kinds of requirements you describe (RDBMS integration including Oracle and MySQL, refactoring and/or rearchitecting, e-commerce solutions, etc.) and have on occasion been a consultant doing just what you describe.

I know quite a few Perl consultants as well at various levels of competency, from coders comfortable in the trenches to highly qualified architects and DBAs.

In answer to some of your simpler questions,

• I think hiring a consultant with knowledge of Perl, RDBMSs, and E-Commerce implementations for the architecting of the system would be extremely wise. I would recommend them to handle architecting, design, and code reviews, particularly since you're considering a rewrite at some point.

  I would not recommend using them for project management. Also be aware that you may not be maximizing your value if you spend money to hire someone with an architect's experience and saddle them with alot of coding duties.

  These observations come from years of experience. If you don't have folks on staff with the existing core competency to do what you're proposing (that is, someone who's done it for years and is considered effective at it), you will save your company reams of time and money by outsourcing the architecture and refactoring.

• I would also recommend segmenting your needs, and perhaps hiring a consultant to perform a less-time-intensive task first and evaluate their performance before you use rely on them further. There's alot of signalling during the hiring of a consultant, but you never really know until you get the goods.
• If you don't have anyone with strong Perl, RDBMS, or E-Commerce skills on staff, I would also recommend hiring a consultant just to help you interview other consulting candidates. If you're up-front about their role (i.e., so they don't consider themselves to be in the running for the job), their perspective as a disinterested 3rd part will improve the results of your interview phase considerably.

I'm afraid a response in this forum for some of your more general questions would be far too inadequate given the complexity and general nature of your problem. However, I would be happy to discuss your questions in more detail or provide you with some names of folks who I have worked with in the past and who are both highly competent and possess a high level of personal integrity.

Send me an e-mail (note that you have to replace -at- with @) if you'd like to chat more :-)

Hope this helps!