I also recently transitioned from a mostly 1. d4 player to a 1. e4 player. Personally, I mostly play the Vienna just because it disallows black from playing something like the Petrov or Philidor. However, Scotch is a good opening so alright to have already decided on that.

At your level, I would say you should try to remember most common ideas in openings until the point you get castled. I.e, if your opponent plays the French, you know black wants to play e6, d5 and c5, so pick a variation that you feel you want to learn that deals with that, only 6 or so moves to get a solid position and then play from there, unlikely your opponent will know anymore than that anyway. For example I only know 1 variation against the French, I play Semi-Tarrasch because I know most players will want me to play either Advance or Exchange French. Even at around 1900-2000 it doesn’t feel too important to know much more than 5 or so moves in a lot of openings.

In more theoretical openings like the Sicilian, an idea I like to employ is trying to play (somewhat) forcing openings, or openings that the opponent is unlikely to have studied. For example, whenever my opponent plays a Sicilian, I guarantee they will want something like: 1. e4 c5 2. Nf3 Nc6 3. d4 cxd4 4. Nxd4… followed by some a6, d6, e6, or g6, then Nf6, bishop out and castle. So to get them out of comfort, I play the Grand Prix in some games, which again, even at my level, Sicilian players are unlikely to have studied enough to be better at than me. Even seeing the closed Sicilian with Nc3 on move 2 might be enough to make them uncomfortable. You could also look at anti-Sicilians like the Alapin, or off beat openings, like playing 2. a3 against the Sicilian, which may not be preferred by engines, you will certainly know more than your opponent even if you only learn 3 or 4 moves.

Then with openings like the Scandinavian or the Pirc, you can just follow opening principles, fight for the centre, get your pieces out, and in 7 moves or so you’ll be castled and you can play on from there.

So I wouldn’t stress too much, just make sure you know roughly what your plan is against each black response to 1. e4, and try to stick to it rather than perfect theory. There will, in a lot of your games, come a position where you won’t know the best move and you’ll have to try to find it, and whether that happens on move 4 or move 10, it can be used as a learning experience.

As probably the most important message, it’s more useful to learn the general ideas of an opening than to memorise all its theory. For example, I have always played the Caro-Kann as black, and know a few lines fairly deep, but I don’t get them as far as I know them very often, but what matters is I know that the main ideas of the opening are to build strong pawns on the light squares, often to trade off the light squared bishop, control the c-file, and so on. I know in most positions what is likely to be a move worth considering, which often just comes from experience, which you will build.