Hello all,

I am brand new to the world of bonsai and will attempt this first try with a Mesquite seedling that is now growing in a pot outdoors in Montana.
The plan is to re-pot soon and bring indoors to place in front of a window.
Any advice on re-potting procedures including pot size and depth would be appreciated. My seedling is only about 3 inches tall with 3 or 4 sets of mature leaves forming.
Overnight temps are currently in the 50s F.

Thanks in advance!
Cheers!

Sounds like you have a young seedling. I have no idea what you have, species wise. You are i think using a local mountains name (you are in mexico.maybe?).

If the plnt is local to you, i would keep it outside. Small pots are only relevant for bonsai which for you is a decade or more away. Untill then you shoukd give the plant space to grow up.

Mesquite is a shrub like woody plant that is pretty much located in the south west USA - which means the desert part, not California. For a while it was stylish for for restaurants to advertised mesquite grilled things, but I never saw sense in transporting a pile of twigs 2000 miles to cook with.

Put it in the ground for a couple of years and it probably has as good a chance of becoming a bonsai as several other kinds of plants. I don't think it will grow real fast.

As far as I can tell it is not one plant, but a vegetation type?

I think so. I have only been in Texas once and don't recall seeing one.

A 3" tall seedling might be too young to transplant. It all depends on your vision for the tree. The larger the pot you put it in the faster it will grow and bulk up. It will likely survive a repot if done properly and you use appropriate soil..
There are lots of repotting videos on YouTube. Watch a handful - the things that are done in all or most of them are likely to be good advice. The YouTuber 'The Bonsai Zone' generally repots at least one tree an episode. He's also Canadian, so it might be a good reference for you in terms of climate and what species need what and when season-wise.
Speaking of, since you are in Montana it would be wise to check the USDA hardiness zone of your Mesquite. The quick internet searching I did (I think) suggests that it will not survive your winters outdoors. You generally want to start protecting and kinds of plants that are not hardy in your zone when the overnight lows go below 50F.