It's silly to talk about the criteria needed for sealing bijuu into bodies, since there are several different sealing techniques. Shukaku was kept in some container and has had many hosts before. Kyuubi is in an eternal showdown with the Fourth. There's no way in hell the others were sealed with the Shiki Fuuin jutsu.
There is already a sealing technique in place on Pein's side, and it's that giant statue of his. You know, the one with the eyes.
Also keep in mind, Pein's "motive" for getting the bijuu could be a load of crap for all we know. He did hide the secret of Madara from everyone, after all.