When I first got into bonsai it took me a decade to get my head around the fact that if you want a tree that will finish at say 24 inches tall, you need to shop the section of the nursery that has the 6 to 12 foot trees.
I have a Pomegranate that I did the opposite with, I started with a tiny cutting, and it lived all its life in a bonsai pot. It is my first tree and it is still with me. Its now 41 years old, 16 inches tall and only one inch in diameter. Trunks do not bulk up very quickly at all if a seedling is treated like bonsai its entire life. It is, no matter how ugly it is, my old friend, and I won't part with it. I made all my beginner mistakes with it and it survived. I've posted photos somewhere though search did not turn them up on my first try.
You can do some great trees in an indoor light garden. Ficus, Pomegranate, Eugenia, Nashia, Gardenia, Jaboticaba, and literally thousands of tropical and subtropical trees can be grown under a good light garden.
Sequoia is a full sun, outdoor tree. It is hardy to zone 7 at least, possibly the warmer end of zone 6. If you have access to growing these outdoors, they would probably do better than in a light garden. Depending on your micro climate you might be able to plant them in the ground outside. But if you can't put them out, the light garden will have to do. Jack Winkle from Michigan, grows (or grew, he has to be in his late 80's if he is still alive) Mendocino cypress year round in a light garden and has turned out some nice, convincing trees. Hopefully someone can post a link to the articles he wrote on indoor bonsai. You might be able to keep the sequoia going, if your light garden is bright enough for good results with full sun plants (tomatoes, marajuana or peppers for example) Just joking about the weed.
Grow the sequoia out, bigger than your final plan, get them big and bushy. This may take 3 or more years. Then you can do your first styling. Right now they are too sparse to cut anything. they need all the foliage they have to get them to bulk up. Get some other species to work on while you are waiting for the sequoia to bulk up. And read articles, forums, books and such in the mean time.
Shop at a florist or nursery for Ficus or Pomegranate, or some other tropical tree, look for specimens with trunks in the 2 to 4 inch range, they may be more than 5 feet tall, don't let that worry you. Bring them home and chop them down to fit the light garden, That's the fun part. Key is start with a thick trunk, and reduce the tree to size. This technique will get you a convincing tree much quicker than start small and growing it up. Best to shop with a tape measure in hand. You want a tree with some low foliage that will be left after chopping to fit the light garden.
In your reading look for articles mentioning the use of sacrifice branches. You will have to use this technique to bulk up the trunks of your sequoia.
And welcome to the forum. Bonsai is can be a rewarding life long hobby.
