How do I use the locale module?

I'm preparing the conversion of a site (all HTML flat files currently), which exists in multiple languages (currently: English, French, German, Spanish, Russian, Italian, Bengali, Hindi, Portuguese, Farsi, Swedish)... of which I plan to do the major languages first. I have been eagerly awaiting 4.5 because of the locale module, so that I can distribute PO files out to my translators.
However, I am a bit perplexed as to how it works.

As I understand it, when I export a PO file, it will do a "gettext" on all the modules installed on the site, and export the result. So this raises some questions:

1) It seems to me logical that I should have to install all my modules on the source site first, before doing the export to PO. I presume that if I install a module AFTER doing the export, then when I import the translated file back again, the newly installed module will not be translated.

2) Is it worse than this? Does something bad happen if I proceed like this:
a) install Drupal core
b) export PO file
c) install module 'X'
d) import translated PO file

Thanks for your help...