I would like to use 29 or 30 red cards to reliably imprint a color onto Chrome Mox. I have the same concerns about Mox as you which is why I was adamant that the card in Fortune Thief's spot be red and non-artifact. My list currently has 27 red cards which is less than I'd like however I believe that the Serum Powders change the math somewhat.
I kept several hands with Serum Powder although I believe I took a new hand more than half the times I opened with them. In goldfishing this was not the case, but in the tournament it worked out that way. Serum Powder saw play if it was keeping me from getting Hellbent or if I needed to get to 4 mana. I remember that my primary discard fodder for Gathan Raiders was Powder, Mox, and Land.
My feelings on this deck is that the game is won or lost in the first 2 turns. Whether or not that is true, I keep that in mind when deciding to keep or throw away a hand. I look for a hand with 2 hosers and the mana to resolve them. Ideally this is CotV and Blood Moon. I'll also keep a hand with 1 hoser and 1 threat with the mana to play them. The hands I throw away are usually all or no mana.
When I look through my list I see ten spots that are "flex". They are currently:
2 Flametongue Kavu
1 Thundermaw Hellkite
2 Bonfire of the Damned
2 Serum Powder
1 Koth, of the Hammer
1 Umezawa's Jitte
1 Fortune Thief
Of them, the only ones I wouldn't consider other options for are Koth and Jitte. I like them both as 1-of's because they are never forced to sit in my hand that way. I am faithful that WotC will eventually print another mono-red planeswalker that will be good in this deck... The problem with cards like FtK and Bonfire is that they are either all-stars or dead cards depending on the match up. I would prefer to run Phyrexian Revoker main deck but we run into the Chrome Mox problem again.

