The message
from "Simon" contains these words:

I've got two 14 metre Leylandi (I know, I know, I didn't plant the damn
things) at the end of my small garden. I want them chopped down to a more
manageable 5 metres. I'm in the process of getting quotes from local tree
surgeons. The one I spoke to this afternoon plans to climb them, presumably
using climbling gear, and segment them from the top. As my garden is small
and access is difficult, this seems reasonable.

Are there any questions I should be asking apart from the obvious
(insurance, cost, time, removal of wood).

Maybe ask him for a local client's reference for similar work?

I asked to see our contractor's insurance certificate before he started
work, and he didn't mind at all.He recently removed 6 similar conifers
safely from our new garden using the same technique as yours suggests,
cost £15 per hour; gave me a good estimate of time beforehand, and did
an excellent job. We're on an island with fairly low pay rates compared
to urban areas.

Does the plan to retain the bottom
5 metres as a screen sound reasonable, providing it is regularly trimmed?
Any rough guides on cost?

I wouldn't recommend that as a permanent measure, it'll look hideous;
I know because we did that too :-). All but one tree, were felled to
ground level. The remaining one shelters our raised oiltank from strong
wind and the neighbours' view; so I had it cut to 5 metres, as a
temporary measure while I grow a replacement screen. As soon as the
hedge screens the tank, the rest of the tree will be felled.

Janet.