Strategy for 5,10,15 and 20
For 5 and 10 silver, just put any overseer / warlord you have, and add Abe. If possible, borrow inventor Eugene at the max. He helps a lot.
Put Abe on spot number 4, inventor Eugene at 1 or 2
For stage 5 gold, have your strongest Abe and company team, and don't forget to turn off the auto button. Select your own ultimates when they're available.
For stage 10 gold, put Abe on spot number 4, Kate on spot number 3, Sophia on spot number 5. If you got magna and legendary Eugene, put them on 1 and 2. Rinse and repeat until you killed the Frontline first