Some questions about being an O/O

I read Nightwind's post and found a lot of good info in it. But I have questions that weren't in it. I'm driving for USX but only for the expeirence. Before getting my CDL I was self employed as a contractor but the days of milk and honey are gone here in Michigan thats why I went into trucking. Being used to being my own man I have a plan and that is to some day be an O/O but I am ignorant to some of the basics.
How many miles can you expect from your tires ? How much do tires cost ? How many miles can you expect from an oil change and lube ? How many miles is too many miles on an engine ? What is the cpm's that you charge and does it change on weight ? And if you cant get a contract w/ a shipper what brokers are dependable and can that keep you busy plus make money ? I have seen Landstar but they require 1 yr otr and at this time it lets me out. This isn't something I'm going to do tomorrow but some day and I like to research it as much as possible before shelling out a lot of money. Also do you use the brokers trailer or do you need one of your own? I know, theres a lot of stupid questions but unless your born with this knowledge you got to ask them. Thanks, Jake