Yeah, there's no such thing as a Newb Friendly Monster Hunter game. I've been with the series since the original Freedom on PSP and I got reality checked HARD by my first round against Yian Kut Ku, embarrasing as that is to admit, especially now that I can kill it in less than a minute. Weapon wouldn't pierce, he ripped right through my armour, I didn't understand. Then I took the time to get into the mindset of a Hunter and it all clicked...been addicted ever since. Just handed Gore Magala his arse in a doggy bag.
As for starting off, my advice, go with 4 since as others have said the underwater battles are a pain in the arse in 3, even with dual analogue controls they're still slow and kinda boring. Besides, 4 has a greater variety in the fights so far, more monsters, more gear, it's just the better choice all round. The Sword and Shield is a good weapon to start off with until you feel ready to experiment with the different weapon types. Watch a few tutorial
vides on Youtube or something if you get stuck, there's a lot of people out there who are happy to help bring new players into the series. Stick with it and once you get past the initial hurdle and develop that mindset, you'll find one of the most rewarding games ever made. Don't worry. I had to go through that trial by fire and so did pretty much everyone else, we were all newbs once.