The amount of opening preparation that's useful for a sub-1700 is minimal; diminishing returns due to not understanding middlegame positional ideas and shaky tactics hit really hard. When I was really into chess as a kid ~15 years ago, I spent a ton of time reading opening preparation but it was definitely time that I should have spent simply analyzing high level play in all stages of the game because my opponents either didn't know the theory (so while they technically deviated into "worse" lines, I had no hope of understanding why they are "worse" in the general case) or more rarely, they know how to avoid common theory.

I think the most important opening prep for a novice is learning what lines to avoid at all costs. A lot of this, though, can be established with the basics: develop pieces, castle early, control center. Any time your opponent tempts you into violating any of these, think thrice.