I want to become an O/O

Yes and no is the best answer I can give. First, answer these questions (not out loud).
#1 Do I have $20k in the bank right now?
If not, can I save up that much?
If no, stay a company driver.
If yes, go to step #2.
#2 Do I want ALL the responsibility for EVERYTHING that is involved with the truck?
If no, stay a company driver
if yes, go to step #3.
#3 Do I understand how to manage time, money, personal communications, education, money, time, money, time (see what I did there?) effectively.
Start with those. Then we can ask the hard questions.

 

HOS is not even part of the equation.
Your question there scares me a bit, here's why:
3 years of driving you should understand how to calculate fuel consumption. I have homework for you. Spend the next 30 days tracking every drop of fuel you put in the tanks to the penny. at the end of the month, take the exact number of miles driven and divide it by the amount of fuel purchased in gallons. now also divide the amount spent on fuel by the same mileage number.
This is costing 101.

 

Between 3 and 9 mpg based on operation. Whether its a worthwhile venture depends on you. Some guys go broke out here. Some net 150k+ a year.

 

That will tell you on average how much you spend in fuel per mile for that exact truck. Here's the kicker, no 2 trucks will get the exact same MPG. Why? good question. Tire size, driving habits, differences in roads, loads, idle time, maintenance, etc.

 

Yep, that is lesson number 1.
Lesson 2 (this is harder) spend the next 6 months tracking every penny spent on maintenance on that truck. Every tire, road service, PM, repair, light bulb, scale ticket.
This will give you a base operation cost when you divide all that stuff by the number of miles over that 6 month period.

 

Lesson 3 involves the cost of insurance, taxes, salary, truck payment, parking, and more.