How do I answer that! I can write a book on this and not even scratch the surface. If I can throw you some tidbits of advice for a total noobie, I would say first of all, spend a couple hours looking through the GW website. Before you even start caring about how the game works, you need to decide if you are serious about going into it. Then figure out what models you like the most. Don't worry about what is good, what has the best fluff, what armies win the most tournaments. Worry about what YOU like. You will be building and painting models that you pay a LOT of money for. Make sure you are doing it for the right reasons. The first tank I ever bought was the Vindicator because I thought it was awesome. I went with Space Marines because I remembered all those old pictures from when 40k first started of the beaky marines in huge combats. I wanted to collect them! I do Blood Angels now because I love assault marines, and red is my favorite color. So go with that first. If you like anime aliens in mech armor, go with Tau. If you like Ripley Scott aliens infesting planets, go with Tyranids. If you like Starship Troopers with hundreds of grunts pounding the ground and dieing like gnats, go with Imperial Guard. They are all good.
Start small. Buy yourself a SINGLE SQUAD. Assemble and paint it. Then get another. A transport or something. Build your army slowly. DO NOT collect an entire army and stack the boxes on your shelf or worse open and assemble them all. You are a long way off from playing full games, so don't worry about a full army. Aim small... figure out what is in a 500 point force and build that army. Then learn how to play with it.
Find a friend. Get some one else into it with you. Two noobies learn faster than one nooby and a vet. When I started learning Fritz was teaching me, but I came to rely on him knowing the rules and I was learning poorly. It was not until another nooby and I got together at my house and we played the game for like 8 hours, lookign up every single rule every single time. That is the only way.
Look up every single rule, every single time. Thats right! Do not be afraid to look up rules. We learn through repetition. Do not be embarrassed, but do not let some one who knows more about the game rush you through learning the rules. Ask for explanations until you fully understand them, then do it again.
Thats about it for that! Follow those rules and you are well on your way.
Quick advice. Your list relies too much on good luck and terrain to win. Sanguard are a poor choice as a troops choice since they will die. I would drop them for another large assault squad, and drop the vets for an honor guard. Attach Dante to the HG in the raven. Get a transport on the table to provide at least some mobile cover for those circumstances where there is none, and march across the table. That will improve your chances. However many guys you have, expect to get less than half of them into combat. If you don't think you can take out an entire army with half of your forces, than rethink what you are playing! :)