Posted: 18/01/2017 at 15:36
It would certainly be worth checking with local nurseries and garden centres to see if they can suggest local designers. We used one years ago, purely to help with the planting and to put our loose ideas on design / landscaping onto paper. The cost wasn't huge and we were given vouchers towards stuff for the garden. Once you have some names, call them and explain what you want to do and get a sense of cost before you decide whether it's worth doing or not.
Not all designers go over the top, ours most certainly didn't. What we received was a plan of the garden with planting layout. She came up with a number of ideas that we wouldn't have thought of. It was then up to us to implement as much or as little of the plan as we wanted.
The spacing she put for the planting was for mature plants but she also suggested where it would be helpful to increase planting density if we wanted it to look mature more quickly.
Looking at other people's gardens first would certainly provide ideas for plants, but unless you know their soil conditions, exposure, orientation etc it would be very easy to waste an awful lot of money on the DIY process too.
Whichever way you go, transforming a large plot isn't going to be cheap.