Rhubarb thrives in quite moisture-retentive soil rich in organic matter, often in semi-shade - clay is the ideal soil-type.
Blackcurrants fruit on the wood that grew a year previously. Therefore hard pruning means you may be at risk of removing the fruiting wood. For blackcurrants it is recommended to remove a third of the bush to the ground every year, always removing the oldest third. Gooseberry bushes are a little more difficult as they grow on spurs, so avoid cutting everything back and focus on removing whole branches. Additionally try to cut down on feeding the bushes, slowing growth and therefore minimising the necessity to prune.
Flowering is often a sign of stress or distress - in this case harvesting before the plant is established. Take the flower stem out and keep the plant well watered and manured, and don't pull any more sticks from it until it is well established. Rhubarb flowers are very beautiful - Rheum Ribes, the Syrian rhubarb, is a wild species grown just for its flowers.
Celery is usually planted at the beginning of the year under cover. It needs to be sheltered from the wind, have continual moisture and very rich conditions and it must be protected from frost. A good idea is to put a box around it and fill it with sharp sand or leaf mould, which should keep it protected from frost. Another method would be to create a raised hot bed.