I've just migrated all my stand-alone WP installation to one multisite. I merged users and metas so...yes, it was a pain in the neck!
Expecially regarding user_roles: I had to tweak deeply directly on db level.
One of these website has a woocommerce instance on it. After a bit of pain, it works now. But with a (minor?) bug.
As Super Admin, if I explore the list of users for the website hosting the store, only standard WP user roles are shown (admin, author and so on). Woocommerce ones (Customer, Store admin and so on) are not. As a matter of fact, all my customers are shown as not having any role on the website, which is wrong.
If I check the user list at website-level (not network level) custom roles shown and users are correctly linked.
I'm wondering if perhaps I forgot to update some option here or where to align the network roles in respect to websites ones.
tnx in advance and have a nice week,