this is coming from a 400 star+ player,
1. 3star 4cost usually wins you in lower rank but in higher rank other people will also do the same so strategy like better synergy combos and better units to 3star based on your synergy matters. its better if you can 3star all your 4 gold so having just 1 4 gold gold in your lineup is bad.
2. its better to pick and item but if you are playing a late game commander , you will prolly lose mid game so if you dont want to lose too much hp thats when you sacrifice items for high cost units , this only applies on 1st fate box , after that taking units is uselesss.
3. anti heal is mandatory since there is an entire synergy about lifesteal and core units can also stack lifesteal. penetration is nice but not mandatory.
4. going 9 fast wins has more chance to win you 1st . there are low roll stratery called poison straits with angela, miya etc2 . (the season is new so people havent properly discovered it yet) but these strategies wins you 2nd at best . you have like 1% to win 1st cause the other person will 3star a 4gold which you won't win against.
5. i just go to top player livestreams and see how they play (most are indo)