Keep out of frost while its in bloom. You can plant it out in the garden if you want to, but not before the risk of frost is past.
As for pruning an older hydrangea, assuming its outside and its the common mophead one, wait for signs of growth to show, then clip off last year's flowers and any dead wood you can see.

Yes, and don't "cut back" further than just deadheading in March to the highest good buds on the stem. Cut much deeper and you will lose the current years flowers.
Many people recommend using an ericaceous compost for blue flowers but for pink ones an ordinary one should be OK. You might be best with a soil based one (eg John Innes no 2) if its going to stay in the pot.

Thanks for information.