How do I integrate with identi.ca/pump.io/tent.io with the possibility
of migrating my data?

1) Store most of the original data.
2) Solve identification problem: in my case, use subdomains of
cascardo.info for each service and keep those after I "migrate" working
as gateways.

3) How do I get out of identi.ca and keep my friends subscribed to me
and my subscriptions? Do I link to my account in there and repost? Many
people are getting out, so this may be a chance to get them to subscribe
to my original accounts.