How to play a dredge deck

Hey all, just wondering if you can give a newb some advice on how to *play* a dredge deck. I copied what aww1979 posted in his tutorials, shown below, and I feel like I need an instruction manual.
1) What should I be discarding when I use Bazaar? Bridge from Below is obvious, but what's the priority for everything else?
2) Should I be dredging every turn to return Golgari Thug, Grave-Troll, etc. to my hand?
3) How do I avoid decking myself from the dredging?
4) Would adding some threshold cards and mana be a smart modification, or would it break the dredge engine too much?
Thanks for any advice!
.398 4 Bazaar of Baghdad
.684 4 Golgari Grave-Troll
.678 4 Golgari Thug
.680 4 Stinkweed Imp
.681 4 Narcomoeba
.705 4 Bridge From Below
.700 4 Dread Return*
.666 4 Cabal Therapy
.1531 1 Angel of Despair
.675 4 Flame-Kin Zealot
.691 4 Ichorid
.682 4 Unmask
.449 4 Contagion
.1851 4 Pact of Negation
.120 1 Iona, Shield of Emeria
.576 2 Petrified Field
.1913 4 Dryad Arbor
1) What should I be discarding when I use Bazaar? Bridge from Below is obvious, but what's the priority for everything else?
2) Should I be dredging every turn to return Golgari Thug, Grave-Troll, etc. to my hand?
3) How do I avoid decking myself from the dredging?
4) Would adding some threshold cards and mana be a smart modification, or would it break the dredge engine too much?
Thanks for any advice!
.398 4 Bazaar of Baghdad
.684 4 Golgari Grave-Troll
.678 4 Golgari Thug
.680 4 Stinkweed Imp
.681 4 Narcomoeba
.705 4 Bridge From Below
.700 4 Dread Return*
.666 4 Cabal Therapy
.1531 1 Angel of Despair
.675 4 Flame-Kin Zealot
.691 4 Ichorid
.682 4 Unmask
.449 4 Contagion
.1851 4 Pact of Negation
.120 1 Iona, Shield of Emeria
.576 2 Petrified Field
.1913 4 Dryad Arbor