i'm interested in purchasing a few tree's , but need a little guidance.

I require something that will provide privacy from people walking along a
raised communal path that runs behind our rear garden fence. there is
currently some screening at either end of the fence from tree's on the
public side of the fence (they look like silver birch. tall thin with whispy
small leaves ). this leave approx a gap of around 25 feet wide to fill (
planting on my side of the fence.) The rough criteria are as follows :

1. it would need to grow to around 20 feet minimum ( to provide the screen )
but i would not want it to grow much higher than 30 feet when fully mature.

2. our garden it quite small 35 * 35 feet approx and so i would want the
tree to grow upwards but not to grow out back into the garden area too much.
for this reason i presume i need to look at a few "smaller" thin tree's.

3. i quite like the idea of the tree having lots a small leaves providing
the coverage as this would be appropriate to the surroundings.

4. it would be nice if the branches and leaves did not begin until around
the height of the fence ( approx 7 feet ) from the floor.

5. i would like them to provide cover for a large part of the year if
possible but am not interested in a fur.

6. ***** the quicker growing the better.....

the soil is mainly clay based but the drainage is very good due to a french
drain running alongside the public side of the fence.

can anyone give me any options

thks