indipendent from any level, you can place immediately 2 farmers in the backline and then get 25 credits to spend on a mine, putting you to an early money advantage, then get one arcer when the second girl appears (if she is futher away by at least 4 tiles), after that you can wait for the 2 girls in one lane and place a bowman and a mine, mines are very good as a first defence against rushes, and you can steam roll it, then DON'T use the barrels at the start, they cost way too much for being good, i suggest to use them when you have at least 6-8 farmers, use them on the Witches and as a last resort if a lane is compromized, Most importantly, for 2-X levels, always put a mine somewhere in the lane, Witches have way too much health and try to eco everything,
A good strategy for dealing with witches is that if you have gold to burn, place a farmer or knight in the front of your furthest unit as the witch blows her magic kiss, then remove the unit once they are charmed. Yes, you can remove them while they are charmed, it is handy for deflecting the stun, and removing the stunned unit prevents him from getting "bullied", which takes away from your overall score, thus allowing for a high profit of Gems with "deathless" strats.