I think rookies might be too expensive right now. My late first rounder is using up nearly 4% of the cap! That's 4th highest on the team. As a point of comparison, my 99/99 WR just signed and extension worth about 5 million a year, which is what the rookie makes this year.
Maybe a top 5 pick should make that much, I don't know, but as reference, in FOF only maybe a dozen vets take 2% of the cap each. More than 2% is for big stars.