you can cut 1-2 mox diamonds and +1 crop rotation easily. mox diamond is horrible in multiples and past turn 3. Its nice to have the extra colored sources but conditional cards arnt great. I could see that strategy working but its unlikely that they will buy more turns than discard or counterspells. Ultimately you just want more turns to play more lands. It's nice that they also hurt combo decks. Nether void is the other card that helps in buying turns. Really its probably too CMC expensive but it can buy a lot of turns.
Yes I feel I can cut down one mox diamond and one thorn for one more top and crop.

Top with tomb is ok and cutting one more green source makes me want either an other green source or top but I still think I am a bit low on green source maybe I'll cut one factory for an other green source.

Sphere gives way more time against combo decks than discard this feel obvious to me but is weaker against a larger variety of decks, in particularity thorn.

Yes I am on the BG color the red/white/blue other colour doesn't really matter but I think red is the best for pyro/reb/grudge/pyroclasme which I might switch to.