Running Broken Ambitions might not be too advantageous although it fits with the theme of the deck. The reason I think is because of the necessary clash feature. Millfolk really doesn't have too many 'I win' clash cards readily available. Also, with running 20 Mana, do you think you'll have enough to cast Cryptic Command when it matters? Perhaps the most potential counters could be Familiar's Ruse, Sage's Dousing, Rune Snag, Cancel, Spell Syphon, and Dream Fracture? Spell syphon might work well if you get your merfolk going and it's really cheap too. The reason I argue for dream fracture is that it 'kinda' thins out the player's deck by 1 more card w/it's arcane denial-esque drawback and nets you a card in the process too.
If you're only going to run 20 land than yes, cryptic command could be risky, but its also very powerful as it lets you bounce something in a pinch, tap all their creatures to perhaps prevent an all out attack, and can draw you a card. Dream fracture is very good in my opinion, and if you aren't going to run cryptic or broken ambitions, than running sages dousing and dream fracture would counter stuff and help you draw to what you need, so those might actually be the better play for you. I'd think about fitting some grimoire theives in there somehow though, those things can be a real beast plus useful counter at times, and it has great synergy with memory sluice. Memory sluice and conspie with two theives= mill 14 for one blue. If you ever decide to splash white, judge of currents is a must.