Yes, planting now is fine unless there are a lot of frosts forecast! Put A LOT of well rotted manure/compost in at the same time as hydrangeas are very very greedy feeders. If you are choosing a shrub hydrangea, the usual rule is to plant them on the sunny side of a shady border if that makes sense
Oh yes, and never, ever prune old flower heads off until last frosts have more or less passed, even if you see it budding. Then prune back to a pair of buds ( a single bud will be a leaf, a pair will produce a flowerhead).