I want to grow herbs in the house such as Thyme, Rosemary, Basil and Sage. What's the best potting soil to use? And, where can I order the seeds or plants to get started?

You can't go wrong with miracle grow potting soil with most plants. Exceptions being cactus, succulents, orchids, and others that don't like regular soil, but I don't know of any herbs like that. As far as seeds, unless your like me and just like the challenge of growing from seeds the I would by the plant from walmart, home depot, lows, etc... and you can get seeds at all of these places without a huge shipping charge too.

i use Miracle Gro Potting Soil, and have had a lot of success. You may still be able to purchase plants (herbs) at a local nursery.

Rosemary grows well in regular soil. I do not know where you are writing from (location, weather, etc. I am in California and it is used as a landscape plant which requires very little care. You can buy it at Home Depot, Orchard Supply, or any stores selling plants. I found it did well in a planter, but did better in the ground. The same is true of sage--I am not sure if it needs to be a particular variety for cooking or if all varieties of sage are edible. Sage does not like a lot of water--after all it comes from the desert--so it doesn't need maintainance. Usually you can buy seed packets in the same stores for herbs such as parseley( likes moisture) basil and the rest --- on the packet of seeds it will tell you how to grow them and when to plant if they are going outside.

Best wishes for a tasty garden. One of the beauties of these plants is that they smell wonderful.