Follow this guide, and download the free Commander deck building template to learn how many lands to put in your Commander decks, how many ramp spells to run, how much removal you need and much more
I think you should go ahead and snap up the Phyrexian foil now, or in the next 1-2 weeks, before the price shoots back up
That wraps up the additions, so whats getting cut
Black is important to setup cards like The Infamous Cruelclaw, Felix Five-Boots and Prosper, Tome-Bound that synergize nicely
The first mode will always happen before the second, which happens before the third, and so on
Flower acts in the same vein as Traverse the Ulvenwald because of the Flourish half being a powerful spell in the lategame, so long as you have some creatures lying around to pump with it