Thymus Plugs

I am planning on using the lower prostrate forms of Thymus for ground cover in my 2500 square foot back yard. In Anaheim California we have enough of sun and growing period to use it as all year with no frost. I am interested in using various thymes as swaths of ground cover. Will the various types comingle and revert back to wild thyme over time?
Please let me know how many plugs to plant ? Does each variety have a different spacing between plugs? The types I am interested in are the one to three inch mats, like lemon carpet thyme or creeping thyme.

Since creeping thymes eventually cover large areas and do so at different rates, your original scheme will soon result in the more aggressive varieties overwhelming and crowding out the more slowly growing types. I would suggest that you separate the various varieties by pathways that are rigourously kept free of any plants. If you aloow a great carpet former such as creeping thyme a foothold in the lemon carpet thyme area it will soon crowd and choke out the lemon thyme and it will seem that the plants reverted back to the wild type when all that happened was that the wild type choked out the less aggressive carpet formers.
The spacing recommended for the initial planting should be on six inch (fifteen centimeter) centers or four plants per square foot. The more aggressive plants will close the spaces between plants more quickly and will soon require only minimal weeding, while slower growers will need to be weeded much longer but will provide a more unusual and different looking mat, even if it takes a little longer.
If the varieties flower at the same time some hybrid seed might be produced, but the seedlings would not really have much chance of germinating, since the parent plants form too thick a mat. Any seedlings will probably be much inferior to the parents and the only ones succeeding at all would be rather aggressive seedlings. If you notice undesirable seedlings, I would suggest that you weed them out.