New to Growing my own Herbs

I planted Italian basil, dill and sage an outside garden this year. When should I harvest basil and dill to dry?

Harvest basil when it is about 15 cm high (6") by cutting off the top third of the plant.
If you want dill weed for dips and sauces, then harvest as for basil. If you want dill seeds for pickles, then wait for the fall when the plant goes to seed and then cut off the seed head when it is ripe.

I am also going to order herb plants to grow in my new sun room. I know very little about growing herbs.I cook with them but now want to grow my own. I am considering stevia, spearmint and thyme. Will these herbs grow potted? Do you have suggestions of herbs to grow indoors? I use about all cooking herbs and have room in my sun room for up to 10 plants, depending on their size. I was hoping to pick herbs that would grow all season indoors. I will wait to order until I receive your picks for easy indoor growing.

Stevia and thyme will grow indoors just fine as long as you have a sunny window or a windowsill with an additional source of light such as a fluorescent lamp.
Spearmint should be grown in its own pot, because it would try to crowd out the others.
I cannot think of a common cooking herb that would not grow in a sunny window, but tarragon and chives need to be given a one month freeze out of doors in the fall to prevent them from gradually losing vigour and dying. Any annuals you choose will last longer indoors than out of doors, but will eventually have to be replaced. Biennials such as parsley, where the first year growth is the kitchen herb, will last much longer if protected from any frost, but eventually they will lose patience waiting for winter and just bolt to seed anyway!