Hi Paul, I think now is a good time to plant your trees/shrubs. However, if you want to plant bare-rooted specimens (which certainly seems to be the cheaper option) they will be more widely available in the next month or so. Your planting scheme should consider the type of soil (clay/loam/acid/alkaline (lime-rich) etc) and conditions (sunny/exposed/dry etc) that you have. Do you know? A picture of your site will help.
Suggestions:
Pyracantha - flowers, berries, cover, nesting sites. Evergreen. Will survive most soils, but a waterlogged site is a definite no-no. Otherwise, this is one of my favourite plants for the wildlife garden with the added benefit that it is fast-growing.
Hawthorn - has the added attraction that it is a native plant and supports around 150 insect species. Not evergreen, but really easy to grow.
Guelder Rose - native and tolerant of moist soil with a high pH.
Holly - native evergreen great for nesting birds and hibernating insects, and supports the gorgeous Holly Blue Butterfly
Buddleja - the "butterfly bush". Not everybody's cup of tea, but "does exactly what it says on the tin".
You might want to plant something with a more open branch structure to hang feeders from and provide perches for birds, like a Silver Birch (which can provide a sunning focal point), Rowan or a cherry tree (Wild or Bird Cherries are good for wildlife gardens, I believe).
Any walls and fences can be made more wildlife friendly with trellis and climbers:
Ivy - easily grown from specimens already native to your area by taking cuttings. The flowers later in the year provide food for Red Admirals and a whole variety of other insects. It's evergreen and provides shelter and nest sites for birds.
Honeysuckle - flowers for moths followed by berries for birds.
Bramble - supports a whole variety of insect species and excellent cover and berries for birds.
Clematis (Traveller's Joy) - dense branches provide shelter for nesting birds. Very easy to grow from seed collected at this time of year and lime-tolerant.
Climbers provide almost instant height to a new/bare garden.
Best wishes with your new venture, and the move
!
Ash