My main criteria as a user of the system were that it should be MARC compliant, and allow for editing of all MARC fields, have a user-friendly search interface that allowed for Boolean searching and have a web pac that was not too expensive. I did not require a serials or acquisitions module. The reports may not report on what you need. Try to impress upon the sales representative that you understand all systems to have glitches and that you would like to know of the glitches before purchasing the system. One way of doing this is to ask about upgrades that are being planned for new releases.
Nasty surprises seem to be par for the course, however.
There is bound to be a minimum of 6 weeks turn around for even the smallest collection and for larger collections it will be a lot longer. You should be careful about choosing the vendor. Decent cataloguing is a must. I would suggest employing an assistant to do the copy cataloguing. You will not need very high level assistance - it is usually as simple as typing in an ISBN to pull up the matching record.