Talking acreage, a potentially useful book to read/have is “5 acres and independence” by M.G. Kains.
Some of the older editions have good references to horse drawn gear, it’s use and usefulness.

How much land can two people work by hand? It depends on the kind of land and the kind of work.
For instance, working as a team two people could, with practice, reap (with a cradle-scythe) and bind up to an acre of wheat, or two of oats in a day.
To double plow, harrow and seed an acre (using a single furrow horse-drawn plow) might take a day or might take two. To do it by hand with hoes or mattocks would take a lot longer.
On the third hand(!) if you had a crop like rice, and could broadcast over clover and then flood the paddy (no till method as in ‘One straw revolution’) then you might reasonably expect to work a lot more land.
EDIT: amended to add that this chap takes 6 weeks to cut and bring in 6.4 tonnes of hay from his 5 acres using (usually) 2 people and a scythe

[ May I preface this by saying that VERY FEW people are truly self-sufficient from their land, making and producing Every-thing that they need there. More often perishable items that are hard to transport and store (like fruit and leafy vegetables) are grown on site, and some form of transportable specialty (or more than one) is engaged in.
This might be, for example, raising a swine heard on oak mast and turning it into <span class=”st”>Charcuterie </span>, growing bulk grain, growing root crops or onions or field beans, It might mean having an apple orchard and press and selling/trading hard or soft cider, or a milk herd and making cheese – you get the picture I’m sure!]
You can essentially approach the issue two ways (as I see it; YMMV);
1. Decide what kind of work you want to do to make your money, then find the right amount of the right land to suit. This approach is dependent on you knowing precisely what you can do, or want to do, but offers the advantage of tailoring your land choice to your skills and needs.
2. Get the land you can afford (or look at that which you have) and see which activity/s suits it best and work as much of it in those activities as you reasonably can.
In this approach work for your land to make it work for you. If you have steep hills don’t try and grow grain on them; plant fruit trees or nut trees and collect them as they roll down hill to you! If you have flat aluvial land consider grain or dairy, but if it’s colder perhaps oats or rye might be the better choices for you.

In any case, if you find you have more land than you can utilise (by hand, or with horses) in your chosen activity, then my suggestion would be to plant it in mixed coppice (including some nuts and some standards) and leave it be; this will then be an asset that will provide game, firewood, timber, poles for fencing, charcoal and any of the other ‘greenwood crafts’ that you care to name.
It can be used by you and yours, or rights to it’s bounty auctioned/traded off to others for minimal management.

I hope this is food for thought :-)
Best wishes,