Now, I was brought up in a carpentry shop; my father is a master craftsman in a number of fields, and he's had various work areas. The only thing they've all had in common is copious space - these are not sheds and basements, they're full-on professional spaces where you can build a 10-metre stairs and rotate it without running into anything. I'm not thinking of anything that big, not least because I'd never have the use for it. The largest things I'm likely to handle are more on the 2.5 metre scale.
There are two key aspects, I think - working space and storage space. And the two cannot overlap. The default state of the place needs to be that the working space is empty, and the storage space is full, or nearly so.
The working space in my father's shops has always been big, heavy tables. These would have tops a good 4cm thick, maybe more. 2 metres by 3. Legs in 10cm square chunks of timber, often braced two ways. They weren't nailed or bolted to the floor, because sometimes they'd need to be moved, but they were incredibly immobile pieces of furniture. And then they'd have a full sheet of thick plywood attached on top, because the working surface would become pitted and battered, and need to be replaced after a while.
Now, I'll never need anything quite that massive, but I do reckon that something very solid is essential. If you need to really put pressure on something, if it's clamped down, the very last thing you want is the table moving. There's a heavy desk that was in the house when we got it, and is now in the garden shed, which might well be ideal for this job, except that it's far too low - any surface that's comfortable to sit at is not comfortable to stand at. So it might be best to build myself a bespoke worktable, at the proper height, and with the proper density. I think a 1 metre by 2 surface should be plenty. 1 by 1.5 might even suffice.
The worktable also needs space around it. A metre would be good, but I'd probably get away with 75cm. That would, on a 1.5 metre-long table, give me space enough for an object of up to 3 metres in the longest axis.
Now, there's the question of a vice. A good vice is essentially an immovable object, so common sense dictates that it be attached to the worktable. But it can get in the way, and having taken so much trouble to ensure that the worktable can remain clear, deliberately putting a heavy chunk of metal where it can interfere seems counter-productive. There are two possibilities, I think - you either ensure that the vice sits slightly below the surface of the table, or you put it on a second bench. In constrained spaces, I think the former is probably more likely.
Then, storage space. There are two kinds of storage spaces needed - tools, and materials. Tools need to be visible, accessible, and safe. Wall-mounted racks of one kind or another are ideal for this. Boxes are definitely not; they encourage rummaging, and rummaging in a box of sharp things is trouble. There is also, of course, something very pleasing about a wall covered in tools. Tool storage like this isn't even all that intrusive; it doesn't use up much space in reality.
Material storage is another matter. Materials for projects under way, bits of scrap that are "too good" to throw out (and I've been really glad to have these, already), and then the things like sandpaper, glue, screws and nails, varnish, and so on. That can take up a lot of space. In some workshops I've seen, there's an entire room, sometimes a second building, given over to this storage. Again, that's not practical for me, so I think that stacking by a wall for timber, and a cupboard for the sandpaper and screws end of things will be needed. Maybe some semi-loft-like storage, if the structure allows for it.
Is that everything? Not hardly. There are three other things to consider: permanently placed tools, lighting, and ventilation.
Permanently placed tools are the things like table saws, pull-down drills, sanding belts, and so on. At present, of course, I've none of these. A pull-down drill would be convenient, but isn't essential. Some sort of mounted saw would be very good, though - not necessarily a table-saw, but one of the pull-down style as well, perhaps. And maybe a small lathe. And, considering how much of my reference material is online, I'd need space for some sort of laptop or old desktop computer. These things need their own space, usually along by a wall. Some of them need a solid bench, again, for a mounting. They do need a workspace, but they can share that around the main work table, and if they're on benches, then I might have drawers or other storage underneath.
Lighting is a thing that my father's shops never did well, but I'm not sure that lighting was done well anywhere in the 80s and early 90s. What's needed is one or two powerful pendant lights over the main work table, high enough that they won't be hit by ordinary movements. And then you want spot lighting for the permanent tools and storage spaces. There's no need for these lights to be on all the time, and indeed, if they're off, you can get the pleasing effect of a pool of light in the working space, and nothing elsewhere to distract.
And finally, ventilation. My mild allergy to wood dust seems to have decreased massively in the last couple of years, but it's still better not to be breathing it too much. Not to mention varnish, paint, and glue. A flow of air is often enough - so a door and a window will do. I'd like to have some sort of air suction, as well, for clearing away dust from places where it'll otherwise build up, under saws and drills - it's entirely possible that an old vacuum cleaner will suffice for this.
Ideally, then, I'd be looking at a space of about 2 metres by 4. It would, of course, fulfil many of the functions of our existing sheds - storage of garden tools, outdoor furniture, and so on, and I'm sure the lawnmower can find a space in there someplace. Inevitably, some compromise will be needed - but it's nice to have an idea in mind.