It's very difficult here to tell what is happening, so it's best to take it to another shop for a second opinion. Don't tell the second shop what the first one said until after they diagnose the issue. Good luck!
Is it an engine noise? Is the oil pressure light on?
You'll need to find the source of the leak and address it. What kind of help do you need?
5 volts should be the reference voltage from the ECM to the ECT, do you have that? The voltage signal that goes to the ECM will be lower, and that may be what you are measuring?
This is indicating that the transmission computer has identified an issue and is flashing the OD light to warn you. There are many possible issues that can cause this, so it's best to have a shop perform a diagnostic check on the vehicle. If you need a shop, look for a RepairPal Certified shop near you: http://repairpal.com/volvo-within-10-miles-of-43140 Good Luck!
I agree 100% with pushrod. If there are no issues that could point to dirty injectors, then this is not needed.
Your note is contradicting itself. "Engine cranks" and "turns over" are the same thing. When you try to start it, do you hear the starter spinning the engine?
The sensor identifies when one of your lights has stopped working and turns on the brake bulb warning light. This can often be the cause of the brake lights to stop working. Check for power coming into the sensor from the brake light switch, if you don't have power, check the fuse and brake light switch. If you have power, check for power going to the brake lights. If you have power in and not out, replace the sensor. Hope that helps, good luck.
Setting the crank and cam timing requires special tools to line everything up. Did you use these? Are you getting any codes?
This requires some testing to see what the issue is. I'm not sure why you replaced the cat, but hopefully it wasn't for this issue. I would start with checking fuel pressure. These models have issues with the fuel system, so start there. Or better yet, have a professional look at this so you don't waste your money replacing parts that are not needed. Do you need help finding someone qualified to take car of this for you?