Before it goes to far we need to know were you want to go in the industry.
Do you plan to get into the wheel house, engine room, or stay on deck your whole career? The sooner you know the sooner you can start getting your ducks in a row to start moving up the line.
Do you want to sail around the world on a tanker or container vessel, working tugs that move barges and ships around, the Gulf of Mexico working in the oil and gas industry delivering supplies and people to platforms and rigs, or *shudder* cruise ships were you work with tourist?
How often do you want to be away from home? Months, weeks, or days? Same can be asked for time off.
To answer some of your questions:
You are correct in that you need to get your TWIC first. Then an MMD if your going to be on anything over 100 tons. Then your BST. STCW does not equal BST, but a part of STCW. Although everyone thinks it is. BST is only 5 days. The 9 month thing on that dudes website is not necessary, although there is a program like that at the Merchant Mariners Academy at Kingspoint.
All of that seaman's book and medical stuff if strictly blue water stuff and is handled by the unions if you go that route from my understanding. But yes they are seperate from the CG form as that is what you have to get filled out when you hand in your stuff for your MMD.
As for boots only thing you need to worry about is are they steel toed and can you ware them for 12 hours. Don't worry they will be scuffed up and dirty in a few weeks just like everybody. Its the guys who's been "working" out here for a while and his boots are still new looking that I worry about.
There is a good thread of on what to bring on your first hitch, so look that up for info.
You will start out as an OS on deck most likely. Don't worry about the rest.
As for finding work, where do you want to work dictates how you find a job.
Sorry to ask you more questions and not answer very many of yours, but getting your head spun around and being confused is part of the game. Just wait until you decide to start getting your license the the fun really begins.