1 and 2 - See how
everything is possible in this world. I assume that the Pareto principle will work, your 80% of shares will follow the indices. and 20% are against. if you to know a way the index-> you can pour the champagne. if not-> 80% of your shares will destroy your account. even one stock can fall as deep as you cannot even imagine.
Test your idea over the past year for the sake of experiment. but the experiment must be clean. because at the moment you know the direction of the indices for the past year. and you will "predict" the trend. but it would be interesting to see the result.