I am not sure how your device is set up, but on my ti-84 I can have multiple payloads stored. And I just manually switch between them, and just choose the one I want to use. So I guess check through the instructions for your device for that. As far as the managers go, you don't have to use more that one if you don't want to.
Just make sure you check for updates for it so that you can use the new features and whatnot. But you can use more than one if you want. You may want to just read up on a few to compare. If your site says that the downgrade works unlimited, then I guess you should have no problem changing between the ones you need at the time. But I would not do it all the time because there is always a chance of bricking your PS3.
Seems that the PSNHermes is using 4b, so just grab that one. The PSNHermes is here: http://www.ps3news.com/ps3-hacks-jai...to-3-50-final/