Right, haven't thought about cascading. Still, I'm not sure the spirit guides would be good as it's kinda bad when comes to hand (I don't see a lotus petal in this kind of deck being really good, but maybe it is), and is speeds a little bit the clock when cascaded. I agree with you as to accelerants density, but I think the upside of being reusable overcomes the downside of being a bad cascade target.
About acceleration, I don't think BBE is acceleration, since it's very overcosted for a 3-2 haste, I don't think we should consider as if the second spell is free. I'd say the second spell costs 2 mana in terms of card power/cost (3/2 haste seems like something we'd want for 2 mana tops). It's card advantage, but not acceleration IMO.
In regards of tarmogoyf, tbh I was just trying to go another route to not have to spend a lot in 3 or 4 (since BBE's unban in modern it's really gotten overpriced), maybe even find something better. Pyromancer sounds kinda bad in this deck due to instant/sorcery density, goyf seems really betterthan it at least.
It's really hard to get an oppinion of the deck without playing it, as it's so different from what we are used to see in the format. But still, I think scab-clan berserker sounds too amazing in vintage. It's not worth very much when not cast on T0 against shops, and against dredge at any point, but against blue decks it's just awesome when it sticks. I think with 6 0mana accelerants and 4 DRS we can rely on it for turn 2 most of the times, and it sounds enough to consider running 2.
I wish I had the resources to play it now (as tarmogoyf seems really necessary for the deck), I think I'll have it soon and then have a more concrete oppinion about it.