Firstly, this is the Enterprise Guide discussion group, and this posting seems to be completely outside the scope of this group.
Secondly, migration of a company's legacy data is not a trivial task to be covered in a handful of pointers, but requires technical experience and project management skills beyond the scope of a discussion group.
I suggest you research the papers on the subject globally on the web and specifically some of those held from User group conferences on support.sas.com.
Personally I never undertake projects of this scope (but not necessarily of this type) without the benefit of the contracted skills of someone who has had the experience or training to undertake such a project.
Kind regards
David