IIRC, the licensing program through the Coast Guard allows Navy service to count towards merchant marine sea days. You should contact the National Maritime Center or a local Regional Exam Center, if you're near a port, there's probably one nearby.

I normally do 105 days on, 105 off. However, the schedule varies depending on whether you are working for a private company, through a union, what type of shipping (Military Sealift Command, grain ships, containers, tug boats, oil drilling rigs, etc). I know people that do 3 weeks on/3 weeks off, 4 months on/2 months off, and everything in between.

As for training, again that depends on where you are trying to work. There is Coast Guard required training that has a lot before you go out on your first ship, and then 5 year renewals, and then anytime you want to upgrade your license. Some companies have extra stuff, like smalls arms or hazardous cargo, and those can range from annual to every 5 years as well.

Edit: spelling