I just finished a 6000 word article on Legend Handlock play focusing on how Legend Handlock players think about each card as well as expert tips related to each card and relevant matchups. Hearthstone Players made what was originally a wall of text prettier and hosted it for all visitors (not just premium subscribers) to read it for free. I believe it will offer a much fuller answer to many of your questions and concerns. Thank you again for all your interest and support!
The fully updated guide is here -
I'll be updating and commenting there!
Credits to fellow Handlock Legend Trakkyhoon for helping me tech the deck. I ranked up with Handlock exclusively from rank 9 to Legend, and I peaked at rank 469 with this before I started trying to learn Miracle and tanked ranks. My win percentage was around 60% maybe a bit higher between rank 5 to Legend; I only say this because the 500 win counter indicated around 75 wins between rank 5 and legend (speaking conservatively).
I hit Legend on 6/26, so it was a pretty diverse meta - I probably could have hit Legend earlier, but I took a break for about half a week. My deck is teched towards a diverse/unclear meta to be jack of all trades and master of none. There are other variations of Handlock, but this is a variation on the most vanilla/classic Handlock. Handlock is a tough deck to play at its full potential, and I'm not sure about it's place in the meta game - this variation has like a 60% or less against top Legend miracle rogues, probably 55% against the midrange Druid, also like 60-65% against top Legend Zoos.
I watched a lot of Reynad VODs to improve my play, and it definitely improved my play from rank 5 status to rank 1 status. The key thing to remember is to try play more proactively and less reactively (aka throw down your mountain giant or farseer for 2HP gain) unless you're really trying to bait out removal, but the number 1 rule of handlock is still to make sure you're always out of the other deck's lethal combo range unless it's super low probability (they've played parts of their combo already).
2 Soulfires - learning how to Soulfire is also a big part of this deck; soulfire to clear board when you can. This is usually after you play Mountain Giant or Twilight Drake and is recommended unless you have basically the best hand in the world to counter their deck.
2 Ironbeak is important vs Freeze Mage, Control Warrior, silencing Ancient Watcher against cancer/aggro decks to race them/dump cards from your hand. Owl will probably also get better with Naxx's incoming Deathrattle minions.
2 Hellfire is good for most metas where there is aggro around. 2 Shadowflames is nice if you see mostly Miracles and Druids, but if there is any decent amount of aggro, I think 2 Hellfires is better. 2 Hellfires can also be used to deal damage to the face and win. I've closed out a few games with double Hellfire + Soulfire.
2 Facelesses - I really like Faceless for the Leeroy PO combo (it closes out a lot of games), and it's pretty decent in a lot of matchups to copy your own taunted Giants or copy whatever is worst for the other deck (IE copy Twilight Drake versus Priest). I want to play Alex, but I'm not sure how I feel about that. That versus second Faceless is still a debate for me. Alex is marginally useful against Druid for dodging the 14dmg combo, but it's not useful against Miracle Rogue. Alex is a bit better for Control Warrior, but the matchup is not that common and Alex isn't that game swinging other than having another 8/8 (which you can have with Faceless anyways). Alex would shine most against burn/aggro decks, but living to turn 9 is already so hard - it's not really a reliable option. I would rather Faceless copy a big taunter. A good handlock game will have you close out the game within 2-3 turns of having a Giant stick to the board anyways, so you might not even make it to turn 9 or you might not really need Alex on turn 9. Faceless can also often be a cheap/free Giant and offer a lot of flexibility. Sometimes, you just copy a doomguard and try gain more board control. Against control decks, you can also copy Ragnaros and hope to RNG snipe theirs back.
1 Sunwalker - made all the difference for me. I would only play BGH if you see a ton of 7+ attack decks like mirror match, Control Warrior, old school ramp druids maybe. But Sunwalker is really solid in mirror, against aggro and zoo, can't be killed instantly by burn spells, and it offers you a decent midgame play. I have tried Shadow Bolt (nice turn 3, but only really shines on turn 3 otherwise you should just soulfire). I tried Black Knight, but I think Sunwalker is better against aggro. Sunwalker versus a second Shadowflame is tough, but Sunwalker can be better against aggro matchups where you havent drawn many cards. Shadowflame is hard to use when you don't have many creatures in your hand. Shadowflame is also more of a reactive card -Reynad was commenting about how Handlock play needs more proactive play since it's strength is kind of mid-late game. You'll lose in the long run against Control Warrior, Priest, Paladin decks, so it's important to play in a way that wins quickly once you play out your Giants. Sunwalker is a bit more offensive than Shadowflame.
No Bloodmage Thalnos - I tried it, and it's really good for those two dmg Mortal Coils, 5dmg soulfires versus Druid but I felt like it was too inconsistent. You always have to pair it with another card to get value out of it; it felt a bit win-more than a necessity. Handlock's slots are really tight so while it is pretty good, I don't think it's good enough to justify a slot. There are better cards to run in its place.
Acidic Swamp Ooze was great in metas that heavily feature Warriors and Trap Hunters. These are the scariest because they represent easy ways to kill off Giants or consistent face damage. We're lucky that we're not in that general meta now. Rogue weapons are not as big of a deal, and there aren't enough Shamans with Doomhammer to necessarily warrant Ooze yet.
3 versus 4 AOEs: I think Handlock only really needs 3 AOEs - whether that's double Hellfire or double Shadowflame. More than that has made me feel like I'm holding one too many AOEs. Reynad had made a similar comment, but he wasn't sure what was a better replacement for the 4th AOE. I also find that in a typical game it's hard to get the opportunity to use Shadowflame twice. I used to run the 4 AOE build, but I felt like a more judicious use of Shadowflame has been sufficient. Hellfires are also really good for the Shaman matchup. I like being able to play Hellfire on turn 4 and having to be able to tap turns 2 and 3 (or hope to dig into a Hellfire). Shadowflame on turn 4 requires setup and you draw into one less card - thus this means that an early Shadowflame would require you to have a hand mulliganed in such a way to play a turn 2 or 3 creature to prep for the t4 Shadowflame. I like having the option to tap more in case if I draw into a Mountain or Twilight.