I would definitely mix in some compost with your garden soil as this will improve the structure of it. The dusting with fungicide is useful as it prevents the risk of infection, however, if you keep an eye on them and be ready to spring into action then it could be worth trying without . As for planting, I would personally keep them inside for a while, give them a chance to strengthen up before putting them outside in the elements!
Grow your roses indoors, alternatively. You can also raise roses in a greenhouse. You’ll need containers that are at least 9 inches (22.9 cm) wide. Spread 1 to 2 inches (2.5 to 5.1 cm) of small pebbles at the bottom of each pot to ensure good drainage and fill each with halfway with well-draining soil. Plant the roses just beyond the graft point and then water well.
Black Spot: Rose plant leaves with black spots that eventually turn yellow have black spot. This is often caused by water splashing on leaves, especially in rainy weather. Leaves may require a protective fungicide coating, which would start in the summer before leaf spots started until first frost. Thoroughly clean up debris in the fall, and prune out all diseased canes.