A player had a good question.

How much "space" is "space" in Book of Estate?

Especially, he noticed that you can use a horse herd to sell horses. His thought was to expand the current £10 herd, i.e. 24 horses instead of 12, or two herds instead of one. And use one for himself and one to sell horses. I see no reason this would not work, but was trying to consider how much space it takes. In BoE the herd size is mentioned in acres, but investments in simple "space".

For simplicity?
1 space = 1 herd?

1 investment that requires space = 1 space.

So an additional horse herd investment (on top of the one each manor comes with and which is abstracted away) requires 1 space = exactly the available 'usable space' that you have in the normal 10 libra manor.

I assumed if it took space that all 'spaces' were the same. Each manor has enough extra room to fit one of those things. It makes sense in-world since a 10L manor has 10L worth of space. If it had more room than a typical manor it would be worth more due to that additional land.