I also recently completed the process for getting my OUPV, Master, Sailing endorsement, and Towing endorsement. The material that is tested is sometimes difficult and comprehensive, but I was glad to have learned so much. I studied for about 5 months, using an online training school since there were no "in person" schools near me. I passed all tests on the first try, but I studied and practiced my butt off before taking the tests. The school provides the tests at a proctored testing site--in my case, Denver. There are four subtests for the OUPV (six pack), and an additional test for Master, sailing, towing, etc. A lot of people do not pass the "rules of the road" test the first time. It requires 90 percent to pass whereas the others are 70 percent.
The definition for a "day" of sea service is a minimum of 4 hours. If you own a boat and can provide documentation of purchase and continuous ownership of that boat, you can self certify. Anything else requires signature of the actual owner. Any lying about this can result in fine and jail time, according to the instructions. The requirements for sea time is a minimum of 360 days, with 90 within the past three years. You have to specify where you got the sea time--Inland, Great Lakes, Near Coastal--as that will determine what geographical limitation is put on your license. The size of the boats you have served on (gross tonnage) will determine what license you can apply for (eg. 25, 50, or 100 ton).
You need to pass a physical, get a drug test, get a TWIC card (sort of like a TSA card), have a valid First Aid/CPR card, and fill out a bunch of application and supporting forms. I did it all myself, but having someone who has done it before to help you with it is probably wise. The overall cost of the entire process is NOT minimal, with you having to pay for medical, drug, TWIC, First Aid/CPR along with the 145 dollars for the actual application. Any school or testing fees are in addition. Buy the time I was finished, the out-of-pocket costs for me was well over $1000.Once you get all that done and paid for, you then send it all in and wait for about 40 days--if you have a complete and "clean" application package. Any errors, omissions, or questions result in further delay and request for documentation. They do check out the forms you send in. Will I ever use the license commercially? I doubt it. Am I glad I did all the work and learned as much as I did? You bet!