1: No, I had no surplus shards. I used to reroll any shards I got from chests to unlock champs. I didn't care which champ. When preseason was about to start, I had only one shard, so I disenchanted it for the 6.5x BE multiplier.
2: Yes. I only care about finishing my collection. My OCD demands it (and I mean that literally, not as an "it bugs my OCD" meme/joke. I have OCD, among other things, and completing collections is something I'm compulsively driven to do.) And actually, I see no point to mastery emotes at all. I unlocked two, and that was before I realized you could reroll champion shards to permanently unlock a champion. I thought you rerolled three to get a new random shard. So I had the tokens for mastery six Lux/Veigar, so when I got a Lux and Viegar shard, I was like... cool! I guess I'll use the shard for the mastery. Mastery 5 is fine with me. I'd rather spend my BE/Shards on champs any day.
Edit: Actually, if you could disenchant the Mastery tokens or whatever they are called for BE, I'd be VERY happy. I have two Lux mastery tokens, one soraka, one MF and one Leona just sitting in my inventory that I will never trade in for mastery six until I have all the champs and no other use for the BE/shards.
3: Again, yes. I haven't managed to unlock a chest in over a month. So at the moment my only awards are coming from capsules on level up.