As I said in our e-mail conversation, the entire concept of the "Triple Goddess" and "Maiden/Mother/Crone" is a modern one drawn from the book "The White Goddess" by Robert Graves which is a book of poetry. Gerald Gardner picked up on this concept when he developed the religion of Wicca. The MMC concept does not mean that one worships three different Goddesses, it means that you are worshipping a Goddess in her various forms through the seasons (The Wheel of the Year).
There are some so-called Triple Goddesses in ancient lore, but the people who worshipped them did not view them in any way as Maiden, Mother, Crone. Again the MMC construct is a completely modern one.
In Traditional Wicca we worship a Goddess of the Moon and a Horned Lord. These are two very particular Deities whose names are never revealed to a non-initiate in one of those Traditions. We see our Goddess of the Moon as repesenting all of the stages of a woman's life; therefore, Maiden, Mother, and Crone. So one Goddess with three aspects - not three different Goddesses. We generally work with whichever aspect relates to the season of the year. So in the spring we work with the Maiden, in summer the Mother, and in the late fall and winter we work with the Crone. In addition, we might choose to work with one aspect of the Goddess because we are doing a particular working. For instance, even in the winter (the Crone's season) we would call upon the Goddess as Mother if we needed to help with an issue regarding child-bearing or children. There is no jealousy involved because we are still working with the same Goddess.
If you are practicing an eclectic form of Wicca as a solitary then you can work with whatever God and Goddess speak to you. They don't have to have been a triple Goddess in ancient times. For instance, in my personal practice I work with Sekhmet and she was certainly not a triple Goddess, nor was she a moon Goddess. But we have a relationship nonetheless
If you're not part of a particular Traditon you can work with a Goddess of your choice. Same is true for working with the God. I generally suggest that you don't mix pantheons as some cultures didn't get along with each other and neither did their Gods. If you want to work with Vesta there is no reason not to do so. But I would then try to establish a relationship with one of the Gods from the Roman pantheon as well.
You seem to be struggling a bit with the concepts here about both the nature of our relationships to the Gods and that of the Triple Goddess. Here's some books I'd suggest that I think will be really helpful to you in coming to a better understanding of Wiccan beliefs about the nature of the Gods.
"The Witch's Goddess" by Janet and Stewart Farrar
"The Witch's God" by Janet and Stewart Farrar
"Devoted to You" by Judy Harrow
