When you reach the 10th concentric ring of neighbors on your map, you can't clear it catering unless you have orc resources, which requires a tech in the orc chapter to unlock and is the biggest built-in scouting constraint. I didn't fight any provinces from chap 3-6 as everything was always Very Hard because I started in the desert and had to scout so far to reach neighbors. These days, I don't even clear provinces unless the bossy event quest lady tells me to. As
@Gladiola said, it's better to use your troops on tourneys anyway in my opinion.
I would shift perspective on thinking that 3-star troops are your saviors. By the time you get them, the enemies are 3-stars too. I have a fighting city from trying to help my FS get to higher chests in tourneys, which was a lot harder to get to 10th chest in the old system (remember when we had one training slot, boys & girls?). I learned to manual fight out of necessity to stretch my troops out since they hovered at 5x for awhile. Manual fighting lets you see what the heck is actually going on in a battle and observe how AI behaves. Battle is a lot more nuanced than just picking 5 units to fight with that is auto-fight. You can see how terrain and a unit's initiative number comes into play, then weaponize it. Manual fighting mitigates troop loss because you are less likely to fight like AI's idiotic maneuverings, but is a
BIG TIME SUCK though. They do need to introduce at least 3 more speed increases to the game engine to speed through all those unnecessary animations (you can also "hybrid" fight--start manually, auto-fight mid-battle).
I would highly recommend early chapter ELF fighters to go to town on Vallaorian Valor pits (crafted in MA). Heavy range are the peskiest to deal with early chapter. On paper, you can use sorceress, banshee, treant, or Vallorian Valors against heavy range enemies. Unfortunately, Level 1 sorceress and banshee are absolute divas that die if they break a nail. Treants always show up to the battle an hour late because they forget to adjust their clocks for daylight savings so the battle's practically over by the time they reach an enemy to take any swings. Therefore, the gator guys are the way to go, esp getting to those pesky mortar guys that hang out in the back! Valors get to enemy heavy ranges a lot faster and only takes 2 chops or so to get the job done. All those early rounds your treants spent leisurely walking to the battle site, all your other units are getting blasted or mauled to bits, which means more troop loss/replacement too. I had 5 gator pits at one point. Now I'm down to 1 since my mages have leveled up and don't pull a muscle sneezing.
Yikes, the idea that AW/expansions increase difficulty seems a bit counter-intuitive for a game like this where you can spend money.
Number of techs unlocked, AWs, AW upgrades, plots, and premo plots all affect difficulty, but they are weighted differently. For example, you'll feel the difficulty increase faster with unlocking techs than wonders or wonder upgrades. It does mean you have to ask yourself questions like, "Is that Throne of the High Men really worth 24 tiles and will forgoing it mean I need to say affirmations in the mirror each night to feel better about myself because I am potentially ranked lower now in the eyes of my Elvenar peers?"