I don't want to waste time on opening preparation. By this, I mean that I don't want to have to understand/memorize the moves or the typical plans in the middlegame. I just want to develop my pieces, castle the king, and connect the rooks. From there, I wish to wing it, try not to blunder anything, and look out for tactics. Is this enough to reach 2000ELO?
This is an opinion based question as there is no way to know. For Bobby Fischer it might have been, but I met Bobby and know that he memorized all the openings.
Would it work for you?
My tournament experience says no.
These days there are too many people memorizing everything along with all the better training for tactics than when I learned.
Your more likely ceiling would be 1500, with possibly 1700 IF you were really good.
After that, positional play would start to be a factor and by 2000 most players would beat you with traps, better/deeper tactics, or positional play.
And since they do know the openings they would come out of most of them with an edge in position as well as the initiative. So just routine play would give them the edge to win if they were at 2000 already. And if they do not beat you in the middle game with strategy then they will win in the endgame because they are far better than lower rated players at endgames.
If you want to make even uscf 2000 let alone ELO 2000 you will have to specialize in ONE opening for white and one for black and become so familiar with them that you do not need to memorize them as the moves will be obvious because you do understand them. And you will have to be totally fluent with ALL tactical motifs and recognize them in different game settings.
Whereas the question is very opinionated, I assure you this might strongly depend on the player type. (See the recent book of Müller/Engel.) I had a peak ELO of 2350, clobbering a lot of grandmasters on a good day, and this without any concrete opening knowledge. (Sometimes I even invented a new line ten years before it was played in GM praxis, but those ganeffs never give me any credit :-) Your minimum needs: a good intuition and keen tactics. But woe, in the time of computer outpreparation, it probably doesn't work anymore. Especially if you "don't want to know the plans". You won't get away with that. (Imagine just trading all pieces in the Ruy Lopez Exchange.)
Personally, I am 1845 ELO and I have not deeply studied any particular openings. Regarding my middle game, I know some basic tactics (grab any hanging pieces, look for weaknesses, gain space, keep your pieces safe etc) and nothing too complex. however, I would recommend doing only 1 opening i all your games and master that opening to the point where you could create your own traps. However, I would not go as far as to say that you should spend time learning particular traps.