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!
Growing roses from seed is certainly not the fastest method of propagating roses, but I can assure you it really is the most rewarding. However, rose hybridizing is surely a lesson in patience, since your success rate can be very small, and it may take several years to reap your rewards. Imagine opening up presents on your birthday or at Christmastime when you were a kid. Well, that's how it feels to see those little rose seedlings open up for the very first time. You never know what you will find inside.   
As soon as the rose seeds have been removed from the rose hips, rinse the seeds in a solution of purified water (any bottled water will do) with 5% bleach. This would be about two teaspoons of bleach per cup of water. Rinse the rose seeds with plain bottled water in a strainer, then soak the seeds in straight 3% peroxide for 24 hours. CAUTION: Do not mix bleach with peroxide because there could be a chemical reaction.   

Prune the roses. Pruning roses keeps them both beautiful and healthy. The goal is to clear away crowded areas to open up the bush, which helps prevent rotting and disease. The pruning strategy differs according to the season, but the cut you make is always the same: prune just above a bud eyes, the areas where branches form. They look like small circular swells and are usually located above a set of mature leaves. Make a down-slanted cut on an outward-facing bud eye.

Monitor the rose cuttings to ensure they’re hydrated and taking root. Keep an eye on the cuttings to make sure they’re never dried out, as well as to make sure the cuttings are taking root. You can test to see if the roots are growing by gently tugging on the cuttings. You should be able to feel a slight resistance after a week or 2, meaning the roots are growing well.[13]
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