Generally, you can ask for your team to help when enemy invades your jungle, alternatively if your team is being a clown and refuse to help. You can invade enemy team jungle since their jungler can’t be on both side at once. However if you’re in solo queue, also assuming you can’t rely on your team, then your best bet is to identity and lock thier weakest player and snowball from there. Scrap farming / turtle stealing etc.
my opinion bro this is always depends of the situation. you can counter invade enemy jungle if enemy roamer or mid lane is focusing on their gold lane or invading your jungle instead of guarding their own jungle. if you can freely counter invade just go for it. 😊
i build war axe first if i want to sustain/last longer on teamfights and also if enemy got to much tanky heroes. i build hunter strike first if i want to play kinda aggressive at the same time can burst squishy heroes faster. in short. Build War Axe for: Extra Health/Sustain and for tanky heroes Build Hunter Strike for: burst or squishy heroes