Don't worry about the blackberry having only just been planted, it will take no harm as long as you make sure it doesn't dry out. If you get any fruit setting on it this year I would cut the trusses off straight away then the plant can put all it's effort in to putting down roots and so get established quicker. You should get some fruit next year, just be sure to tie in all the new shoots it puts out this year as they will be the ones you will get fruit on next year. Then after that you will be away and should have plenty of berries. Usually the cultivated thornless blackberry plants are less rampant than the wild varieties Just tie in the new shoots every few weeks as they grow and you will have it under control. Be gentle with the new shoots though as they are very easily broken when young which is why I tie them in as they grow. If you need any help just give me a shout.
Thanks Rob!!! You are so kind.