Sorry, once again I'm going to have to burst a bubble. I'm not trying to be mean, I'm just going to tell you the facts - and the reason for telling this is that, if you start trying to grow bonsai, and you find it doesn't work out, it will not help you.
1. Bonsai are rarely grown from seed. Well, actually, all trees come from seed, but starting from seed will take very, very long (think at least 15 years before you have something basic).
2. To grow bonsai, you need the best conditions. The tree must be very healthy and strong. Indoors, you will not find these conditions
3. Junipers do NOT belong indoors. They may live a while, but with the lack of seasonal changes, proper light, humidity etc. they will die
With your reputation as a plant killer, starting with something that requires so much, is probably not a good idea.
Felicidae gave a good tip. Maybe I have one too:
How about creating terrariums? I have one myself. Not as fancy as this one, but it does work indoors, it's fun to do and nice to look at: