Serviceberry will indeed get 25 feet tall, but it will be more of a small tree than a shrub. That's the way they grow in shade. In sun you can train them to be more bushy, but they still don't make great screening plants. Hazelnut will grow more bushy in the shade than serviceberry, but they are really slow growing.
Spacing depends on what you are trying to accomplish. Most shrubs can be set very close 3-5 foot and just grow together and form a hedge. Some make decent hedges and some don't. The problem is that most things which grow well in shade (privet, bush honeysuckle, etc) are things you don't want around.
Good luck....