Take a look at MaRos articles describing new sets - he does not just dump the image gallery and say let me know what you think - he describes the sets design goals, the mechanics, why they were chosen, how those mechanics were placed in each colour, the limited archetypes the set was designed around, some anecdotes about the design process, etc
As for my experience opening the card packs, I opened every pack in the Trove and two booster boxes
Good for an early army launch
In sanctioned play, proxies are judge-issued and the judge decides whats acceptable
There are even some more thematic options in Dalakos, Crafter of Wonders, and Temur Ascendancy, if youre playing blue and green as well as red
That's about it