Is the first picture of little red spikes in the leaf? If so, it's needle gall mite, affects acer and tilia among others, no control that I've come across, just put up with it. Doesn't harm the plant.

The brown could be scorch, if it had come from eg a shade tunnel in the nursery to a sunnier spot with you. Again, not a long-term problem.

I don't think it's time to panic, but I don't grow it, what do others think?

I've only just started growing acers (only because they were cheap in Morrisons) but I'd be inclined to pick off the mite infected leaves and burn or bin them - unless anyone else knows that the mites are good fodder for beneficial insects or birds.

Thank you both. TD, I'm not sure whether they are spikes, more like tiny dots - my picture is a bit blurred, sorry. Although the tree was not in a polytunnel when bought, it may be that I have it in a sunnier spot and it is scorched.
Urban, I think I will do as you suggest - when it stops raining!