Sorry - can't help, but I've taken cuttings too so I'm interested to see the answers from folk who know. :o)

Use some soil from your garden mixed with normal compost. You can add acidic soil if needs be in future to change the flower colour, but that is 3 years away!

Keep the Hydrangea cuttings in a pot in a sheltered spot over winter. A cold frame is best.

Do not plant out as keeping them over their first winter is the most difficult part.

I did cuttings last summer that had good roots by autumn. I put most our in the garden and there was no sign of them in spring and that was a mild winter with almost no frost.

All the cuttings kept in a pot in a sheltered spot next to a wall survived.

I think that you will need to pinch them out to make them bushy, unless they are very tall now I,d leave it until spring. As Kilder says its a few years until you get flowers, you need to concentrate on healthy plants and a nice shape first I think

I agree about keeping them in a coldframe over winter. after that they're tough enough to survive outdoors all year.

Last year I took about thirty 15cm cuttings and at least half flowered the following year. I didn't pinch them out.