@DDK: It depends on what you meta is like. If youplay against a lot of people running CB and Tempo decks then Chalice can make the cut. That is really the big discussion, as to the viability of the card right now. I personally think 4-6 StP effects are way better, but the combo matchup certainly takes a hit ... then again, even back in the old RGb lists w Chalice, combo was still a beating. On of my buddies runs a list w 4 Chalice main and Null Rod in the board and still has maybe a 30-35% chance against combo. He is also running 4 colors and a bunch of "cute" lands for Knight and it seems like everytime I see him in some weird position he is hampered because he has a Maze or Tabernacle in play that can't tap for mana.
The other undecided debate is on Burning Wish. The most common argument against is "its 2 slow" but I'm not sure how an answer-all spell that is never dead and starts to have relevance on turns 1-3 everytime is to slow but ... whatever. I will never understand why people don't run Wish in here but .. its always an option.
All of your questions can be answered by analyzing your meta. What do you expect to see? The best creatures in the deck ... that will never be decided. A while ago I ran Dark Confidant and just despised it but yet some people swear by it. My buddy runs a creature base of: 4x Terravore, 4x Knight, 4x Crusher which he seems to like and, well I don't. The only thing most can agree on is colors, 3 color is generally the best due to the manabase. When playing 4x Wasteland and 6-9 lands that only add 1 type of mana, 4-color manabases are very rough and quite reliant on Mox Diamond. I love the 4-color builds (mainly because I get to run Stronghold) but it sacrifices too much consistency.
Really the only matchups I have written off are Dredge and storm combo. However, storm is entirely beatable with the white Leyline, Wastelands and adequate pressure but its still not good. The Belcher matchup post-board was literally 50/50 when I tested which I was very happy with, but Tendrils is .... not great unless your playing against ANT which is the weakest Tendrils deck ATM. Dredge is and always will be a nightmare for this deck. Unless they mull into oblivion or get really unlucky you are gong to lose. Even if you run Morningtide or something like that in the wishboard ... its doesn't help. But against nearly every other deck in the format you have a great chance and Elves, Goblins, Merfolk, Zoo, Landstill, Team America, Bant, you are certainly a favorite.
@nameless one: One of my other buddies used to run Bloodbraid Elf and totally loved it, but he really only liked it when you hit DD. It can't block anything and live, dies to every form of spot removal and is entirely random in nature. He liked playing it for the LOLs but you just randomly hit Mox or another Loam and after that the creature is largely worthless. When he took 2nd at SCG Orlando he had totally cut Bloodbraid from his list. Is it a viable option, sure, but there are a lot better creatures to play.
Top is a lot better than Scroll Rack if you want to play a card filtering effect. Rack is only good if you have multiple cards in hand while Top is ALWAYS relevant. When you are winning its cool to draw three cards then put shit back on top an dredge them away but its really not entirely necessary. I would run Sylvan Library over Scroll Rack but thats me. Again, I have read a few people liking this card but it really only seems good if you are winning and have a lot of cards in hand. Totally awesome with Crusher but, lets be honest, ur probably winning at that point anyway.

