Now that Exotic Shards are a thing you'll basically need 3 high level characters. Doing Weekly on each for 27 Coins is enough to buy every week's weapon + its corresponding Shard for the eventual upgrade (except Primaries but let's average it out).
If you only have one or two characters you won't be getting enough coins to keep up with purchases and upgrades. Unless the new level 30 Heroics yield more coins, which would make sense.
It's true. I can't do the 3 characters thing.