I have planted 2 acer palantum, I put them in lightly fertilised soil half ericaceuos, partial sun, they like moisture but not too wet. Hope this helps.

Yes you can use part ericaceous and part general compost but since its well established a good general compost will also be fine.

Hi Lesley and welcome to GoY. Your Acer will struggle with limestone soil, it can tolerate slightly alkaline soil but your's would be more than slightly... You have two choices grown in a large container in ericaceous compost or create an extremely large hole to plant into in the garden part filling with good, slightly acid compost/humus, then plant the Acer into and finish filling with the same mix. Plant in semi-shade and out of the wind which can strip the leaves of the tree in no time flat.