Some questions about model making

I've have wanted to make models for a while now,but dont know how ,I have some questions about welp, model making
1.-my main question is, if I for an example find a sonic model from sonic xtreme online,and want to turn it into a md3,can I do it? will it already have the textures? or do I have to manually model and make textures for it?.
2.-if I do have to manually do both of them, what programs are recommended for it?.
3.-how do I actually turn the model (either if I found it online and rigged it or made it all by myself) into an md3 file

This might help: https://wiki.srb2.org/wiki/Model
but you're going to at least need a program that can export MD2 or MD3 with or without a plugin.