1.) What would be my best bet for finding the correct tool life
I do not know about Correct tool life but tool life can only really be determineed by running it until you can see or feel a difference in the cutter edge, chip formation, part surface finish and dimensions being cut.
2.) How do I know when I exceeded the tool life, will it break, will it be out of tolerance by a few mills, ect
If you have exceeded the tool life beyond being dull, at times it may break and your part will be out of tolerance.
3.) Is there a standard test I could run to determine it?
No standard test that I know of mostly due to so many different varibles to consider.
4.) What would be your best guess for tool life with a 1/4" TiN 3 flute end mill cutting a .1" DOC slot into Aluminum 6061 wit a surface speed of 1000, just a ball park here, I know it depends on VERY many factors.
Pretty hard to give you a " ball park " figure but it should last quite a while.
Tool life has always been a mystery to solve for many. When cutting aluminum drilling tools will last for a very long time, so will milling tools but this also depends on how hard you are pushing your tools.
Really, the best way to determine some sort of degree of tool life is to start with a known new tool. Re-sharpened tools will normally not perform like new tools unless you have a cnc tool grinder to re-create the exact previous grind.
Visually inspect your new tool cutting edges with the naked eye or use at least a 10 X power lighted magnifier. Know what they look like.
Use your fingers and feel the sharpness of the cutter. Know what they feel like.
Do these same two things periodically or after every part ran.
Pay close attention to the chip formation left by your first cuts and if you can, measure the chip thickness.
Compare these results to later on when you suspect the cuuter is dulling.
Pay close attention to how much of a burr is left on your part edges.
When these burrs start growing, is a sign that your cutter is dulling.
Inspect your part dimensions closely so you can begin to determine when you are seeing variation.
When you begin to see some part variation you may then also start to see some tool cutting edge changes.
It will also make some difference to tool life if the slots you are cutting are being formed with a tool with a sharp corner or if it has a factory corner radius on it.
The actual effective length of the cutter, the tool holder being used and the rigidity of your work piece also can influence tool life.
I hope this will help shed some light on this topic.