Three of us having helped the widow of a friend dispose of his workshop in the past year I'm very aware of how much effort is involved in this. It's not something that most people would volunteer to do twice.
I'd encourage
@Annette to take up the offers of help with thanks.
The most important thing is to identify any high value items. Advice is most useful here. You will need to make the effort to list them for sale with detail to get the best return.
There are likely to be a lot of items that while useful, are not especially valuable and will take a lot of effort to sell. Try to understand the broad value of such things and be open to offers on the day from people who come to look at / buy the bigger ticket items.
Many buyers have their eyes open for extras and may be tempted.
Realistically, don't expect to get more than 20-50% of the new price of anything unless it's both valueable and in very good condition.
Gumtree, facebook and car boot sales are all options for the lower value items but facebook is full of scammers and car boot sales sadly plagued by petty theft. Ebay the best return for high value items as it reaches the biggest audience. Our for sale forum here tends to introduce you to good people but not bring the very highest prices as buyers are knowledgeable and won't overpay.
It is understandable that you may need machines to be collected by the buyer, but be aware that that will always limit the number of people interested and the cost of travelling to collect means buyers will pay less.
