2000 is an amateur level?!

Its slightly misleading to say you only need to study tactics, maybe until you are a 1500 player but if you want to get to 2000 you need a solid opening repertoire and reasonable positional understanding because the higher you go players just don't make glaring tactical mistakes that allow you to win the game with one shot.

Once you get to 1800 or so studying endgames gives you far more bang for your buck in terms of study time because you can grind out wins in drawn positions or save theoretically lost positions against the majority of players who have no idea what to do. Of course there are still tactics involved, even in King + pawn endings so you need to keep doing tactics exercises to stay sharp.

I can say endgame study has helped me, I've got a few wins from  tough win positions and ground out a couple of draws from lost positions. It gives you an aim of how to end the middlegame and makes you more confident in trading to reduce risk and increase your relative material advantage.

I wouldn't follow that advice personally.

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Also analysis of y some moves in certain openings helpful, will be awesome, but when I c grand master games, I really dont understand the reasoning behind most of their moves ..lol'

Join the club!  Many GM moves are too subtle for the likes of me to understand, I've even seen well annotated games where the annotator resorts to 'Black plays a waiting move here' or something when they obviously don't know wnats going on either!

Its impossible to tell somebody what openings they SHOULD play. Really you need to look through a few systems and find out yourself which ones feel right, it depends a lot on whether you like open attacking games or slow positional battles.

I play d4 with White, if Black plays the Queens Gambit I go into the exchange variation because I like slow positional grinds. I have narrowed down my repertoire to one choice each against the Kings Indian, Nimzo Indian and Gruenfeld, theres just too much theory to take on if you want to study everything.

With Black I play the Caro Kann against 1.e4 and the hedgehog against 1.c4 but haven't found a reliable defence to 1.d4 yet, usually play .Nf6 and go into some Indian type position but White has so many ways to play its hard to be definitive.

Thats my basic repertoire as a very dull risk averse player..your mileage will vary.