My first game in the series was Monster Hunter Tri for the Wii and I honestly didn't have to do any research (unless you count looking up what parts of the Monster are weaker). It's very hard at first, you will probably hate it the first 12 or so hours, but after you get that initial hiccup, there's hundreds of hours to enjoy.

Keep in mind you can die A LOT at first (you will fail in general even after "mastering" the game actually), so if you are a gamer that gets frustrated easily, you will probably never get pass the learning curve. 

I started watching a MH 4 lets play to see what kind of things I need to learn.

I actually saw some gameplay of each weapon and I'm thinking Dual Blades looks like it would be the funnest to me.  I haven't looked into the armor sets yet.

Edit: also I found this http://monsterhunter.wikia.com/wiki/MH4:_Dual_Blades_Weapon_Tree

Say I make a fire type weapon, will it be not as effective against some monsters and make the weapon basically useless?  If that's the case I'm thinking of going down the Akantor Blades path so I don't run into that problem.

This. I got into MH with MH Tri on the Wii. I didn't thought about, I didn't play online back then and I didn't research things at first. Simply following the single player. Killing my first Great Jaggi needed half an hour, but it was so great seeing the beast breaking down. I downed a lot of healing potions, but I got it down!

Later I started looking up things in a Wiki, like where to find special bugs or stuff like that. With MH3U I started to play online.

The first few hours will be non-user-friendly, and kind of dull.
Stick with it though; it gets amazing before long, and the further you go, the better it gets. Just be prepared for a stiff, unforgiving challenge.

still hoping for a wii u version of MH4

First off, MH isnt a game for everyone, try the demo if you can but even then the demo cant do it justice.

First few hours will be the toughest when you are learning the ropes. The hardest part of this is which type of weapon to use and how to use all combos and dodges/blocks masterfully. Avoiding damage is ESSENTIAL for the tougher hunts.

You will need to do hunting of same monsters as well as gathering/mining to get enough materials to make stronger weapons and armour. Can get tedious but if you find the combat fun then it wont be a chore as you can gather while on the hunt.

You will mainly use a Wiki to research about which weapons you want, which armour set you want and where the rare materials are. Other than that Wikis are really helpful for gunner classes as they take more know how to use.

You will HAVE to constantly change armour and weapon elements in order to dish out more damage while avoiding the most damage you can sustain. You wouldnt use a fire weapon against a fire monster while wearing an ice based armour *shudder* youre gonna have a bad time if you do that.

I like a wide range of games and the combat looks fun to me, so I think I'm just gonna dive right in with MH4 Ultimate and skip playing a demo.  I'm used to looking up thinking on a Wiki, I did that a lot with the Souls series, especially Demon Souls.  

I was wondering, say I have dual blades and I upgrade them into freezing daggers, but they won't be very effective against a monster I need to fight.  Is it possibe to go backwards in the upgrade tree?  And if I do go backwards do I get the supplies back that I used to make those frozen daggers?  

It's the same stuff with more monsters + prettier monsters. I'd only recommend playing it on a handheld.

What's wrong with MH3 Ultimate on Wii U?