It's more a matter of convenience, time, mess, etc. I'm sort of past the phase when experimenting with mixing liquids was fun and interesting, and now I really prefer just buying ready-made liquids as long as I like them. But I probably will take your advice, since the concentrations are specified and I guess even
I can't muck that up too badly.
I mix most of them at 15% in the premixed juices, so start with that and you can't go too far wrong (except the menthol - you'll probably find 5% plenty!) Though different folks have different preferences, so you may want them stronger or weaker; that's the beauty of MYO (mixin' yer own,) - you can suit yourself
Yikes! Makes me wonder what even the diluted concentrate in the liquid is doing to the cart/filling it's sitting in...
It appears to be the essential wormwood oils - high concentrations just don't get on with HDPE. But we're working on it - maybe bring out a low-wormwood version with other bitters, or find other bottles.
It doesn't appear to be a problem with diluted absinthe juice - I have a dropper bottle of absinthe 36 that's a couple of months old (it's a flavour I only vape occasionally,) but there's no thinning of the walls or discoloration.
Carts (PVC I believe,) and polyfill (the standard polyester or polypropylene - I can't comment on the "blue foam" craze that's sweeping the forums ATM,) are fine, at least with diluted juice (I have no polyester foam bottles to test the concentrate on

) - it's only HDPE that exhibits the effect.