To get an idea of what your question is like, describe to me in email format how to tie my shoes while making a peanut butter and jelly sandwich. Assume I know nothing about what a shoe or a peanut is, and assume I have never done or seen either of these things before. Then assume you can't actually see the tools or the shoe or sandwich you are telling me how to fix.
What I can tell you is this: Beer and Pizza. One of you has to have a friend or a friend of a friend who is knowledgeable and experienced, who also has the tools you are going to need to do this. DO go to the library. Do find books on exterior deck renovation and maybe even porches. Learn about flashing and water resistant construction. Learn about foundations and concrete.
Then, have the friend come help you do this. Buy lots of beer and pizza or whatever you can to bribe (make it worth his effort).
Or, hire a contractor and pay for his expertise. He had to learn all of this and buy the tools to do it with. If he does it wrong, he has to come back and fix it. If he makes a mistake and cuts some boards too short, he has to buy them, not you. If you do these things, (and you will) YOU have to fix it, replace it.
This is the most important investment you have that we're talking about. If you really don't know what you are doing, you shouldn't without onsite help.