Hello, I have a bunch of seeds stratifying, and a few seeds that have sprouted and are little baby trees right now. I currently have the babies in regular potting soil. I wasn't sure how long to let them grow in regular soil and a regular pot? When should I start using a bonsai pot? Also when should I use bonsai potting mix instead of regular soil? Answers greatly appreciated!!

You should use a well drained soil, so it can grow roots easily, at this point there's no need for special soil mixes, don't repot this, it's too early, for now, you should let it grow and make sure it doesn't die...
A bonsai pot is years away for this seedling, growing from seed is an exercise of patience.

Do you know what tree is it?

Oh yeah, and be sure to put it outdoors, I presume you're on winter there, so you can put on a less exposed place until spring.

Yeah I'm well aware I'm going to need to let my seedling mature before doing anything "bonsai" . More curious how many years before I should start doing any bonsai training , or repot into a shallow pot, or go for specialized soil. 3-4 years at least I suppose? Should I leave them unmaintained/unpruned for the most part? I've been getting into botany as a whole so I'm excited to watch the plants grow then be able to bonsai them in the future.

The seedling in my picture is a fairy duster (Calliandra eriophylla). I have lots of other seeds stratifying (maple, cedar, oak, juniper).

I'm currently doing everything indoors with a grow light because I live in the mountains and it's currently cold and snowy. Hoping to get a little speedier growth due to growing under artificial conditions. I also plan on keeping all my plants indoors as houseplants for the most part

I dont know about Calliandra eriophylla. But the maple, cedar, oak and junipers needs to be outside most of the year. Bringing them inside a few days in summer does no harm. But if you grow them inside most of the year, you will newer reach that point in time when you need to worry about styling, prunning or repotting.

Why do you say they need to be outside? Is growing with artificial conditions not capable of producing a tree?

No. That is not what I am saying. It is quite possible to grow tree with artificial conditions. Many botanical gardens all over the world do that But if the artificial conditions are adapted to human needs, it will not work for trees from temperate regions. They have another idea of what is comfortable than you have. They needs to go dormant in winter, they like wind, humidity temperature gradient and rain. And, yes. They like sunlight as well althou artificial light can work (not as good) as long as all other needs is fulfilled.

First contact with Calliandra eriophylla, I know that the types of Calliandra here in Brazil are not full sun species, they like shadowy places, as they use to grow here under other trees, and they grow really fast here, like, in one year being well cared, you can already begin to style it... But not all that might be the case, as I just read "eriophylla" are from arid biomes... Our variaties of Calliandras don't like direct sun when it's too hot, I'm on summer here for example, if the sun is high on them, they close it's leaves... So they seem to have some diferent "habits"

You should read about that species and collect some info about them, for example, I just read that this species growth rate is moderate/fast...

Here are two that I got a few days under their "moms"... up is a "Calliandra Selloi" and down is a "Calliandra tweedii"
They're both around 30cm, and I don't think they have much more than a year, while selloi grows faster, tweediis likes more sun...

I love that species... They talk to you, hahahah.

Nice species!

This is one tough pant species, dealing well with drought, and able to survive in a range of light conditions, but needing strong light to grow. What I can tell, they are frost resistent (e.g., davesgarden.com/guides/pf/go/64267/).

In general with growing bonsai from seed, the primary aims are to grow decent trunk and rootsystem. So you need to let it grow, and every few years repot, organizing the rootsystem. Note: I am not sure how sensitive this species is towards taking it out of the pot. It would be worth it finding out before you do intensive rotwork!

I would take these out of the current pot in spring, planting in indvididal lager pots. For good growth you need rootspace. Bonsai pots are only in order once the basic trun & branches are present. They are for refinement, not for growing the initial tree.

Many routes to good trunks exist. From growing in increasingly larger, but still small pots, via large shallow boxes to ull ground. All with their pros and cons. It is worth exploring the internet, and reading up on techniques. Feel free to have a look at some articles I wrote about this, although my website is not complete yet on this: www.growingbonsai.net/growing-bonsai-from-seed/

That tweedii is cool looking!!