Thanks, I'm glad you like it!
Stat Blocks: I honestly just start with what I want a monster to be fiction-wise, then pick a stat block from another monster that works for the party's level. I think CRs should be about the same. I sometimes adjust stats before/during combat based on how the players are doing. I've never really liked the idea of "official" monster stats, since it kind of ruins the mystery if players are too familiar with what they are fighting.
Skill DCs: Same as the official rules.