Once the seedlings are ready to go into Solo cups/3-4" pots, do you use the same potting mix that the plants will have once they go outside in their 5gal pots?
its your choice if you want em in the ground or to using potting mix... Once your plants are outgrowing the solo cups its time to move em into either 1gal or straight into 5gal buckets...
Yes, I use the soil that will be in the final containers.
I start them in a propagator with seedling mix and then put them into 4" containers when they are roughly 2-3" tall and then put them in 5 gal pots when they are 5-6" tall.