I grew roses in my last garden which had sandy soil and was challenging. Roses are hungry and thirsty plants so if you can give them a good mulch of well rotted horse manure at the start of the season that would be a bonus. If that isn't available then chicken manure pellets or blood, fish and bone are good alternatives.
Although they need watering more because of the sandy soil I only fed mine three times a year. In Spring as they started to leaf up (manure at that time if possible), again in late May and then late July with other fertiliser. No later as they need to start settling down for autumn/winter dormancy. I also mulched with home produced compost twice a year. Of course this may be slightly different in your area. On that note it would be helpful please if you put your State in your avatar box for future reference, it will give members an idea on what climate you're growing in.
My own experience suggests roses need three seasons to mature properly and develop strong flowers and stems, so I wouldn't worry to much about the size of the blooms at this point.
Floribunda rose 'Lucky!' Lilac/pink in colour and perfumed.
