Hello, I'm quite new to fallout, I guess.

The only Fallout I played before NV was Fallout 3. I loved it, it was brilliant, but I only played through the main quest (with some side quests) mostly because I wasn't into RPG back then. Dragon Age and ME however changed it.

I have only just finished the Repconn (or so) quest where I send a bunch of num nucks to space with their rockets. ( I bet I will find their rockets in the ground later in the game )

I'm finding it hard to kill enemies, mostly I'm using a lot of ammo (with guns like Varmint and 9/10m) and it takes like 10 bullets an enemy while they are spreading their fire at me and I have to use a lot of aid. I was wondering, what weapons counts as good, and where can I find them in the game, without going far in the main quest? I'm currently exploring South (below Nipton and Nojvac) but I haven't found any good weapons.

I however have Big Boomer which is apparently unique, and I can sell it for around 1.4k! Don't know if it's worth it, I don't have much ammo in it. I found in Nipton a gun called "That Gun" costs 900 caps. Is it worth buying it?

I wouldn't recommend selling any of the unique weapons unless they are pretty much useless to you i.e, the big boomer for a pure unarmed build.
They make for some sweet collecters items later on.
As for your problem, maybe the http://fallout.wikia.com/wiki/Ratslayer could help you out?

The Incinirater weapon is a bit of a beast as you can get it quite early on in Primm, and works well with any style. The varmit rifle is ok, i think the Repeater rifle is better after that.

I got the Incinirater from Primm, but I almost out of fuel. Yes that one is a beast! I burned the heck out of some ninjas that jumped on me in Nipton (I think) and some very very weird chick with a bear hat. How do I get fuel for that thing?
Thanks for the other guns, I'll google them. Varmint is quite awful tbh.

From looking at the Ratslayer, I see you can mod the Varmint! How do I find a silencer and a Scope?

The best way to get the various weapon mods is to visit the gun runners frequently. They usually have some nice ones.

I'd agree, its a bit of radomness involved, i have started a few characters over again & i have seen different weapons + mods availabe at different sellers, even Chat in Goodsprings had different selections.

Also note that a silencer will reduce the damage of a weapon a bit. I'd say you'd be better off getting the Repeater rifle than modding the Varmit.

Mods i have seen so far = Mangnum revolver mod -50% degrading with use. Varmit rifle silencer + scope. Weapon barrel mod to recuce weapon weight.

As i say, its a bit random.

Thinking about exploring the area and get the Ratslayer. It seems good. It's a bit long journey though, I hope it won't be too hard.

Sniper rifles are pretty decent, they can be brought from the gun runners outside of New Vegas.

Got the Ratslayer! Those rats were nasty, lol. Thanks guys.

What about Armor? I currently only have Legion Armor, I think people attack me due to that. Is it true? Is there a unique armor like the Ratslayer?

With regards to the Armour, if you wear clothing/armour which is faction specific like the Legion Armours, NCR Armours or Powdergang clothing/armours then their enemies will attack you on sight.

I am currently using the Varmint Rifle with a silencer and scope I bought in Good Springs. Works well for long distance shooting while hidden, I have racked up 200 kills with it and earned the Lord Death perk. I sat on the ridge in front of the prison and desimated the population outside with it. I really love this rifle I can get a one (sometimes 2) shot kill to the head on most enemies while hidden.

Yes...Found it the hard way. Had an entire town shooting me when having Legion armour. I have absolutely no armor besides them. Are there any places I can find proper armor?

I wouldn't sell any unique weapons unless you really won't use them, you can steal "that gun" from the locked room in the dino, if you don't mind bad karma and if you have the right lockpick skill, just wait till night time, it's on the right side shelf. It's slow on reload and only has a 5 round clip but with hollowpiont or armor percing rounds it works well and you can find lots of ammo for it

you could lower you diff setting or head strait to new vegas, get some real stuff.

go to the hover dam there is two Chinese stealth suits in the office's it has 20 dr and weighs about 20 also gives you +5 sneak it's also unique, I love this armor but there better suits out there. Also find the brotherhood of steel they have power armor but you need training to wear it, they should train you.

kill benny in the main quest and take his unique 9mm pistol," maria" it is a great gun especially when using hp or ap ammo, it's also the best looking gun in the game! It also helps if you get your guns skill up and use related perks

I'm close to the area but have no idea how to get there. It's blocked in every way I go (from the right side, there was a robot but nothing else, and also from the River, no entrance!) How do I get there?

from novac head north along 95 until you get to 188 trading post, then follow the road east till you reach boulder city, head southeast following the road, you'll hit ranger station delta, then follow the road north and you'll be at the dam

Cheers, got it. Got the armor, looks good! Finally a reliable armour.