As it is pot grown, you can easily leave the plant in its pot for a few days/weeks before planting it. Just ensure you keep the plant well-watered, and it gets enough sun. Don't leave it for too long, however, as you don't want the roots becoming root bound.
Your Ilex aquifolium is likely to need very little pruning (or none)- except from needing to remove any dead, damaged or diseased shoots (or any cross shoots causing possible congestion). The best time to do your pruning is during the late winter or early spring, when the plant is dormant.
Though you only need a little bit of annual pruning, your English Holly can tolerate extreme pruning if it does get too large or overgrown- but make sure to do so during the dormant period (winter months).