The peat will add nothing, suggest you simply use ericaceous compost and grit. Make sure you make the planting hole much bigger than the rootball so that there is acidic soil for the roots to grow into. All acers will grow in acidic soil but not all will grow in alkaline soil, clay they are not particularly fond of so beak that up as much as you can.

Phew, I wouldn't recommend planting them out right now in summer, it'll be difficult to keep them supplied with enough water, much better wait till October (in the South) or September (in the North). As for ericaceous compost, its not really necessary - they don't require acid soil, they just don't like limey, alkaline soil, will be perfectly fine in neutral soil. If your garden soil is limey and alkaline, some ericaceous compost isn't going to be sufficient to stop them suffering, but use some if you want. If your soil is heavy,then adding some horticultural grit is a good idea, but the best addition otherwise is composted material - your own garden compost or composted manure from the garden centre, worked in to the area before you plant.

Your right Bamboo, garden compost or composted manure from the GC far better than ericaceous compost and, definitely don't move at this time of year. If these are the small weeping acers they may just need potting on into bigger pots in autumn.