I had the same problem with Hearthstone on my phone a few days ago.
After the update, it was around 5+ gigs, but after I uninstalled and restalled, it was back to being around 3 gigs.
I've managed to save over 5k gold just from the daily quests. This was through the course of the Taverns of Time event, and the Fire Festival. As long as you're diligent about it, it is possible to buy into the new expansion every time, from just the in-game gold.
For your situation however, you'll get 3 packs for free from Blizzard when Boomsday arrives, and that plus your 3k gold, along with the daily mission, you should be able to get most of the commons, and a good percentage of the rares, with a few epics, and 2-3 Legendaries. If you want to play everything new, you'll need to open roughly 20-30 more packs, and that'll only guarantee the rares (for the most part). Some Epics and Legandaries will always elude you, but that's just the game, even for players that pay.
I would agree Paladin is the most likely next candidate. Rogue 2nd most likely.
edit: For the misinformation being put out, Shadowreaper Anduin is not, and has never been a below average card, even after the nerf. Anduin is still a staple in Control Priest and Quest Priest. The reason you don't see it as often is not because Anduin became bad, but there is much less representation of Priest being played, compared to before. You see it less, because you see Priest less.
Highly splashable/game changing: Bloodreaver Gul'dan - Frost Lich Jaina - Shadowreaper Anduin - Malfurion the Pestilent - Deathstalker Rexxar
Below average/only fit in certain decks: Uther of the Ebon Blade - Valeera the Hollow - Scourgelord Garrosh - Thrall, Deathseer
The only one I could argue for both cases would be Valeera the Hollow, but ultimately the results speak for themselves. She doesn't immediately change the board state, and while she provides great value, not all decks will include her.
On topic: I think Uther, Garrosh and Thrall are all tied for last place. (People can order the 1st worst, to the 3rd worst, however they want) Just think about the situations when someone plays Frost Lich Jaina against you, to where the opponent plays Uther of the Ebon Blade. When Jaina drops, you know that unless your deck has enough burst to win relatively quickly, you're in a for the long game. When Uther drops, you're not scared of them getting a 2/2 every turn and a 5/3 lifesteal weapon; even the "exodia wincon" was obvious a long time ago.
I play a lot of Thief Rogue, and ended up planning multiple end game wincons, aside from just Tess. I took the deck to Wild, and turned it into a Thief + Deathrattle Rogue, It's much funner as you get to play with Swashburger again, and a second bomb late game with N'Zoth.
Even in Standard, you can get "other class" cards via Elise the Trailblazer and Lich King. Recognize that the Rogue matchup will happen, and plan for it.
There's two different types of BM, imo.
There's the definitive kind, where there is no excuse for their behavior. Examples: Opponent has lethal on board but chooses to fool around before winning (wasting time). Another off my head is roping intentionally, to annoy the other player.
The other is one is based on perception, such as the opponent emoting a "Well Played" dealing lethal. Most of the time, the opponent will use a "well played, thank you, or greetings" upon winning, and more than half the time, it is done with the intent to tilt the other player. Of course this is not the case 100% of the time, and so that's just how you want to interpret their intent.