I wouldn't cut back as the plants are just getting established.
When you say your border is big, how big - length/width approx. Is the border in sun/shade which way does it face N/S/E/W? (Sorry about all the questions
but you will get better advice the more detail you can provide) What's your soil like - lots of builders' mess if its a new build! - clay, sandy, stony? Are you coastal, up a mountain and exposed, sheltered and in the SW etc?
Do you have a wooden/wire fence or hedge etc at the back of the border?
What would you like your garden to be like? Any colour scheme in mind? any style - courtyard, cottage, wildlife, formal...
Any plants you like and definitely want or plants you have seen locally that grow well and can't identify (post a photo and someone on here should be able to identify it for you)
Lots to think about - don't be put off; look at lots of other gardens in the area and that should help you see what grows well in your area; it'll also help you see what you do and do not like...look forward to hearing your ideas 