I have no idea about new decks but theres a few different strategies I've seen for getting started. (PS Always grow your daily rewards out to the full week, you can get over 100 seals sometimes (I got like 130 once).
Some day use your seals and buy gold/xp boosts and just power your way up to level 10,15,20. Those milestones give a lot of gold/cards. Then once you are there can worry about spending your amassed seals now that you sorta know what you want from opponents smashing you. (Don't rush up ELO early, just puts you at a wall at 500 and 1000 ELO vs decks that will clown on you.)
The other is just depending on the deck you are trying to play, focus early on buying reinfocement packs for the base set, or for certain factions, buying box/packs of the newest void. If you are really patient it's more cost effective to save up to get the 1000-3000 seal box's especially on special. Don't run multiple accounts because you'll just end up with awesome orange cards all split out and you can't decide which account to love on.
It is quick enough to blaze a new account through campaign and grind multiplayer to hit like lv 5 and have enough for a box or two, and keep doing that until you get an account that had a good draw from the boxes. (IE the right rares/legends that are for the faction you'd like.)
The forgotten wars I think will be gold not seals for packs after todays new expansion release.