Came back from long time not playing. Which is a good hero composition now a days and what should I focus on?
This is my current heroes
To be fair with you: only if you are willing to completely mow down your entire layout, you are not going to get anywhere near the top. But you can get pretty strong with the heroes you currently have. You could try to get your current heroes up. The layout you're using right now has been solidly helping me for a very long time in a fair amount of situations. You are, however, going to need solid hero aids. Nowadays, Storm Rider, The Berserker and Enchantress and some other heroes for other specific situations will make up for the biggest part in the game. Focus on getting a gold Tyrants Brand. Get enchant crystals to get your basic stats up. This should get you started for a while. Good luck out there!
This should get you started with questions you may currently have.
To answer your question:
Yes, get all heroes at least to Leo evolution. But it's recommended to use evolution essences, since you'll most likely going to need all and every single bit of mutagen you can find to improve your hero in the mid to late game.
Personally, I'd recommend working on 1 hero at a time until all heroes have at least skill 20, at least mercenary 30 OR 50. Don't go for anything in between because the cost curve is very odd after 30. I'd recommend starting on Abyss Demon. Don't go for his mercenaries yet. It's all about his main skill which should be focussed to get to 20. Then get The Berserker to skill 20, Enchantress to 15 and Blockhead aid to 15 as well. This will be the most efficient setup for Abyss Demon for a relatively cheap price. The Berserker aid works good at 18, but not in its optimal state. The combination Enchantress and Berserker is what you'll be using for a good while before the game gets very complex to counter even them. But this is what I'd recommend for now. Then get Great Sage skill to 20. If you like Battle Royale, 25. Get his mercs to 30. Then Ambrosia. Skill 20 works good enough. But if you like Battle Royale, again, go for 25. She also greatly helps against enemy healers. Get her mercs to 50. Landslide is an odd one out, but when done correctly, can become a key hero. Invest everything into his dodge and hp. I prefer dodge over hp, since Abyss Demon then needs less time to heal him back to full and the results of hp/dodge investments are about the same. Still, if there's no dodge available to you, get his hp up. Ravager aid should do the trick in mid-late game if you'd like to get his divine through on defense.
Now, I haven't mentioned anything about the all powerful Won Ton you got there. That's because this hero comes down to personal preference. Use him as a main hero and you'll need to focus on getting his dmg output in 1 attack up. If you want to use him as hero aid for Landslide, then this is where it'll become a bit in a gray area. But he's amazing as a main hero nevertheless in Arena.
I hope this helps and happy clashing!