One thing you could do is go straight to the hardest part and see if you have any hope of playing it, or even learning it. If the answer is no then put it aside and work from there.
It is often good to learn a piece from it's hardest parts, rather than just diving in from the start and having 10 pieces that you can play the first 20 bars and no pieces you can complete.
Tempo is quite a big deal, if there are a lot of notes and the tempo is 60bpm, it is unlikely you will be as challenged as you would the same piece at 180bpm so check tempos and timings also.
As pianoplayer mentioned the reality is a lot of notes or a lot of chords is going to be hard, it is often the case that hard pieces are just faster combinations of the things we can already do at a slower tempo. If you can't do it at a slower tempo, use the ideas above to find an easier piece.
Also, with Youtube and other video media, you can tend to find the pieces you want to learn, atleast to hear them and see if they sound difficult.
Lastly try googling "grade 1 piano pieces" you are likely to find a lot of compositions that are considered grade 1 which is entry level piano playing and work from there (grade 1-grade-8)