Moving house after 34 years

Hi all you experienced people.
Once everything is in place we will be moving house.
Some of you may have read my posts about my OCD husband and his difficulty in sorting his 'stuff'.
I am more at ease with this He does manage a couple of hours, in total, each day, so he is trying.
But, and here's the real problem now, it's 34 years since we last moved house and this time in reverse---from a 5 bedroom to a three bedroom, with so many patio planters to be transported, contents of a shed and a potting shed as well as household contents---all to go.
Furniture doesn't worry me, its just the whole idea of the practicalities.
Any good tips please
We are having a full packing service from a reputable company but the whole idea troubles me greatly.
Also, what about actually arranging the removal firm for the date agreed by everyone in the chain. How on earth does it work?
Panic setting in