If you just want to render your models, Studio Max is extreme overkill. Remember, Studio Max is a $3,500 modeling, rendering and animation package. Do you really want to spend $3,500 just to do renderings? There are other options available. Keyshot would be a good alternative if you just want something for rendering. Blender is another option, and it's free.
1. Studio Max Design and Studio Max are the same price, so it doesn't matter which way you go as far as cost is concerned. But if you will be doing architectural modeling and rendering, Studio Max Design is the one you want.
2. I don't like Cinema 4D. I don't like Lightwave either. I've been working with the trial versions of several programs lately, looking for something different, and I've found Modo to be a really amazing program. I like it better than Studio Max. And it's much cheaper.
3. I don't know of any online training. I'm sure there are classes, but I've never checked into it. I would suggest purchasing some books and training DVD's. You can find lots of training material from companies like Gnomon, Digital Tutors, Lynda & Eat3D to name a few.
4. Yes, it's possible to teach yourself. That's how I learned. It just takes a lot of time, devotion and practice. It can get very frustrating at times, but eventually you start figuring things out. Studio Max is a very complex program and has one of the steepest learning curves of any program, other than Maya that is. I've heard Maya is one of the most difficult programs to learn.
5. Don't worry about asking questions. That's why we're here.