There’s actually little reason in general to farm higher Stages, and certainly not if you need to use items to do so.
8-7 is the gold standard for most farming as a default, because it’s the highest Recruits per flag of anywhere in the game.
5-8 is also popular for being a good source of Adventurer’s Kits, aka Backpacks.
The Guide you linked is indeed profoundly outdated. This is a far better one, which is being currently maintained and constantly improved: Barry Farmz Here -- Comprehensive data driven farming guide for Season 3, Season 2, Season 1, Elemental Chests, Atlantis Rises, Missions, and more
I would recommend you not worry about progressing farther on the World Map for now. There’s little benefit to doing so.
Don’t buy heroes in the Shop, they’re a terrible deal. I mean the offers that include some 3* heroes, sometimes with some items.
A better approach, if you’re dead-set on using Summons to get more heroes, is the Elemental Summon, which rotates between elements every couple of days in a fixed rotation of Nature => Holy => Dark => Fire => Ice, though the timing is specific to when you started playing.
Since you’ll most likely get 3* heroes from the Elemental Summons anyway, a better strategy is to just work on upgrading a Training Camp to Level 12 or 13. At Level 12 it will produce guaranteed 3* heroes, and at 13 it has a small (~5%) chance of producing 4* heroes.
I’m just quoting this again to save you frustrations later with this advice:
DON’T SPEND MONEY TO SOLVE PROBLEMS IN THIS GAME IF YOU DON’T WANT TO SPEND A TON
This game is long and very slow — while it starts off quickly, you will soon find yourself making slow progress for weeks and months to come.
That’s the nature of the game, and how it’s designed.
The obstacle you’re currently facing is the first of hundreds to come.
If you spend even $10 each time you encounter such an obstacle, you will spend thousands of dollars. And some of those obstacles would be far more expensive to overcome by spending alone.
The slowness of this game is the game.
You will be perpetually waiting on resources and heroes for years to come. That’s how the game is designed.
Spending money can moderately accelerate that process, but it can’t completely eliminate it, even with 10s of thousands of dollars of spending.
For context, here’s what $17k USD can get you.
If you are going to spend some money on this game, the best deal by far is VIP, as it will accelerate your building progress, and give you additional resources.
For someone looking to spend very moderately, it’s the only thing I recommend spending any money on.
