I recently grew a red maple from seed after cold stratification. The seedling is now about 4 inches tall, and i am not sure what to do next! Do i need to repot? What are its watering needs? If anyone could help with basic techniques this would be great. Its currently in a little cardboard pot with bonsai soil, and looks like these, but the head has already gone, and it is a little smaller.
First of all, the picture you have attached to your question appear to be of a coniferous plant, possibly pine.
Assuming you've just attached the wrong photo, if your seedlings are just 4" tall, then you need to allow them to grow some more. I would leave them for at least a full season and repot them individually just before they break from their first dormant period.
Use a good free draining, but moisture retentive soil and water when the soil starts to feel dry.
Hope this helps.