Advices for a total newbie

Hi All,

My questions might already been asked. If so, sorry for the inconvenience.

I am a computer engineer but I resigned because I don't like computer science anymore. My new career plan is in construction and heavy equipments. I have a close friend. He has a construction company. He offered me partnership. We are planning to but couple of excavators and loan them out whenever we don't use them for our own business. Since this is completely different area of work, I wanted to get to know this as much as possible and I thought it would be best to ask my questions here :) Long story short, here are my questions:

1. We plan to buy +30 ton excavator. Fuel consumption is important. We also want to buy a solid machine without much breakdowns. So, any suggestions?
2. New excavators are expensive so we are looking for used ones. We plan to buy +2012 model and <7000 working hour excavators. Any suggestions?
3. Our first option is Volvo EC 360 (Mainly Volvos). Other options are Cat and Hyundai. Any other "must-consider" options?
4. What should we check when buying a used excavator?
5. Is there any guide for selecting an excavator based on personal needs? For example, my top priority might be low fuel consumption (I heard Volvo is good) or solid body with low level of break-downs (like Cats).
6. Is there any other question that "I" should be asking?

Hope to be among you guys for a long looong time :)

Thank you all in advance.

Regards.

Advices for a total newbie