Argent Squire / Blood Knight is conditional, tough even with card draw. Then again, you are probably drawing cards anyways, plus it's good against Paladin, which I think can be problematic for facerush aggro.
Blood Imp / Young Priestess is sort of conditional. Blood Imp usually better vs Mage. Young Priestess usually better vs most other things. Both die pretty fast.
Flame Imp always belongs. It's too big to pop easily, and has enough power to push field control against most 2-drops and 3-drops. Pretty good for a 1-drop.
Knife Juggler always belongs. 2 for a 3/2 isn't bad, and there's a special ability to boot.
Big Game Hunter is a slow choice, but the decklist in the OP probably can't really push for that super fast GG anyways (not that that's a bad thing). So BGH is probably a good choice. Don't think of it as a 3-drop; think of it as a very conditional card probably to be played on turn 5 at earliest Earth Elemental, Venture Co. Mercenary, Mountain Giant, Molten Giant.
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It's not much good to make recommendations if you don't have the cards to fit the recommendations. I don't have a lot of Hearthstone experience, but what I have seen of Warlock decks goes like this:
1. Facerush. Try to cripple opponent until AOE basically ends you, then hold on to sneak a few damage through for GG.
2. Control rush. Use small minions to control board, using card draw at almost every opportunity to draw into key Murloc buffs and to maintain card advantage. Allows AOE and counters, and gets wiped a lot. Then it just pops three more minions on the board (or more if appropriate which it rarely is) with that gigantic hand advantage.
Way I see it, you're running Facerush, not Control rush. I think Control Rush is superior. Any advice I would be would push towards Control Rush, not Facerush. If you do Facerush, probably try to run off Murloc buffs and Charge. Stuff that gives you card/field advantage like Loot Hoarder / Harvest Golem OK too. Think about using that 5/7 Demon with Charge, since you'll be trying to empty your hand like crazy, and drop crystal costs where you can. For example, Shattered Sun Cleric is a 3-drop that gives something +1/+1; whatever it was is going to die anyways. Run Abusive Sergeant for an immediate 2 boost to attack on an active minion, plus lower casting cost that will let you use Hero power to draw another card. Emphasis in facerush is on aggression, but also on having minions with 2 health or more so they're not easily killed by hero powers and weenie poppers. (For stuff like Abusive Sergeant, the immediate power boost, low cast cost, and its inherent 2/1 outweighs the fragility. Elven Archer doesn't quite make the cut, though.