I would add more land, at least 22 total. Also, maybe some Cathedral of War.
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Some lifelink would fit well so you don't have to worry about blocking. Possibly a few Spirit/Vampire Link, Vampire Nighthawk, or BattleGrace Angel along with Angel's Mercy.
I think you should keep herald and keep doing what you are doing with him. His outlast mechanic helps you build up your numbers and strengthens him for blocking, just what you wanted to do with him.
I really like how you included Guttersnipe, which I think is a good card in this deck. Maybe Lava Spike would be a good addition if you want a sorcery similar to Lightning Bolt.