I don't think you need to shade it. I add compost all the time, I'm not sure if it matters if you do it now or later.

Most finished composts have a NPK value around 1-1-1 (plus or minus 1/2) so it should not be a big stimulant to new growth like fertilizer. One "but" however, check the compost label to make sure that it hasn't been fortified with N, once in a great while soil amendment producers do that to their products. I wouldn't mix it in the planting hole, rather I would spread a 1" layer on top of the soil around the planted rose, lightly scratch it in, water it & then cover it with something like wood chips or pine straw. Usually finished compost dries out very quickly in the sun & because it is fine textured is easily blown around by wind when it is dry. Putting some mulch over the top keeps it from drying out.

Yes now is the time.

Excellent! Thanks for the quick reply. :-)