Cant say anything about Stihl other than I have never had any luck with them so have always used Echo's.
As far as the wood. Try the city or a small town and see where they dump all there tree trimmings. A lot of times you can get some decent logs there. Or try a tree trimmers service and see if they would need some place to dump the logs, etc. You may have to take the bad with the good but at least you'd get free wood. Or maybe give them a carving for some good logs. Don't bother going to a lumber yard. Those guys don't sell logs the buy them.
I have had good luck with the ms 180 as a starter saw, and use my 170 or 180 and an old 025 for almost all of my smaller and medium carvings. I have heard good things about Echos as well. You can consider a carving bar set up later for detail. I have only been doing this about a year and a half and some more experienced carvers might chime in.
I have always carved hardwoods because that is what I have access to. Some say that it is better to start with softer woods like pine but I started with white oak and never found it difficult to work with. The most important thing is a sharp chain.
If you live in a wooded area, there are always some downed trees that your friends or neighbors may let you have. Start with any chunk of firewood and see how you like it. Don't worry too much about mistakes or making your carving "perfect," just keep carving and let your style emerge.
This forum has a lot of good information (especially in the older posts) about safety, tools and techniques...spend some time searching through it and hopefully you can find a lot of information to get you started.
Good luck. Make sure that you use chaps, eye and ear protection.