you know that when you let her have the children more now you setting your self up...
Go with 50%/50% Do not set yourself up to become a glorified uncle. Set yourself up to be a parent of your children. If she says its hard on the children. Then tell her yes her decision has affected the children. One week at yours , one week at her's.
P.S. I would not give her gas money. That is just ridiculous.
Flowers always make people better, happier, and more helpful; they are sunshine, food and medicine for the soul. unconditional love is awesome!