Heel them in until planting - Dig a single hole in the ground and put all tree seedlings in together at a 45 degree angle. Cover the roots with soil. On Thurs pull the whole bunch out and plant. THis will protect the roots, which is all that is important.

Larch are supposed to get up to 25 feet wide at the base.

Not sure what you mean by shrub out. Hemlock can be used as a hedge, not sure if larch will work the same way. Trees forum might be able to answer that for you.