Generally speaking if you can find a duck starter all the better. That said, definitely read labels as availability and products vary... medicated vs not is a complicated one, at one time it was an issue not so much anymore but to repeat reading labels is important as their are variances on what is okay and what isn't that is why often it's just easier to say non.
Many have used all flock, flock rasier though? so not sure what to say with that, i am not in the US so my products are completely different here.
They do look like Pekin to me as well... i have some of those.. feed vacuums lol i have mine on a duck starter right now.. they are sucking that back well... honestly, look into what is available to you within your area.
Welcome to ducks and the forum, love to see updates they grow real fast those Pekins.