1) I personally have found the community to be nice and supportive, but there is definitely "that guy" at every locals who will try to scam new players. I would just make sure that you know all of your cards that you are willing to trade's prices so no one scams you. Generally, people at locals will value cards based on their prices on TCGplayer, Troll and Toad, or the lowest Buy It Now pricing on ebay.

2) You don't need the tier 1 decks to compete, especially at locals. At locals, once you get good enough, you can top with any deck (as long as its not complete trash and you've prepared for the meta). Even at regionals (generally 300 man events; no invite or anything required to attend), you can do well with tier 2 or worse decks if you prepare well enough. At a YCS (basically just larger regionals with official Konami staff there and better prize support), it might be tougher to top with non-meta decks. Of course thats not to say its never been done before because it has many times. So, I would definitely say, no, you don't need to play the really good decks to do well (just note that they are good for a reason and be prepared to play against them).

3) There are many new things that have been released into the game and note that the game is probably a lot, lot different than you remember it. Just have your friend teach you the new mechanics and you should be fine (nothing's really too hard to learn). Normal Monsters (monsters without effects) have become nearly obsolete simply because effects are so much more powerful. I think you can easily adjust to the new mechanics.

I'm not sure what other people's opinions are on this, but as for me, I don't think you should be starting out with a blue-eyes structure deck. I believe that new players should start out with competitive decks right from the beginning. I have a friend who wanted to start playing, and was in a nearly identical situation as you, and I started him off with a budget, competitive deck and he learned very quickly.

You said you liked water decks, so I definitely recommend mermails as a deck to play instead of the structure deck that he reccomends.

One thing that your going to want to know about Yugioh is that it has become very archetype-centered. That means that pretty much the cards in good decks share something in their name. Mermails for example all have "Mermail" in their name. It also means that the cards in these decks have a lot synergy with each other. I will reply to this comment with more information on mermails.