I haven't used the downgrader, but like flashpc said it is currently a one-time thing. So use it wisely. But with regards to the managers and payloads to use. I personally like the OpenManager 2.1I-r2 (or whatever it is called), and multiMAN.
And I use Hermesv4b and PSNHermes v2 (I think that is the newest of that one, if not someone please correct me). The multiMAN and PSNHermes will let you sign-in to the PSN, but be careful since Sony could ban you. I also have read that Gaia Manager is good, but I haven't tried that one yet. Hope that some part of this has been helpful.