Scotland: Change of Land Use Regs

This question is specific to Scottish law, which often differs from the rest of the UK.

I have a dream that now that my partner and I have finally bought a home on a tiny rural plot, I might also be able to snaffle up an adjacant field from some obliging neighbour.
However, there's no point dreaming, let alone approaching neighbours if I would never be able to use that land in the way I wanted, and getting change of use permission for what is currently designated agricultural land is difficult.

Therefore, my question is this: How squarely would informal (non-commercial) smallholding activites fall into the current definition of agriculture in Scotland (i.e. no change of use required)?

I've tried researching this a few times, and always come up against 'The Town and Country Planning (Use Classes) (Scotland) Order 1997' (https://www.legislation.gov.uk/uksi/1997/3061/contents).
This is, it seems, the applicable law, but I find very little mention of agri land at all, let alone a clear definition of what does and doesn't constitute agriculture.

When I look at the regs/advice I find re land use, they explicitly say you can't use agri land as domestic garden. That's a planning permission issue and people who have extended their patios into their fields have sometimes been told to put it all back. But what I CAN'T find is any clear definition re. what constitutes a "domestic garden" vs a "productive garden" (as I understand it, personal allotment gardening would be allowed). My dream garden might look like the former even if I were using it as the latter, so I worry. Reading around, various sources suggest what I wish to do WOULD mostly land within the definition of agri, but not with any great certainty, hence I'd love a clearer view if anyone has already negotiated this stuff.

If my dream is a non-starter, then I want to put it to bed sooner rather than later so that I can focus on how to organise things in the space I do have. Dreams of future possibility is significantly hampering current planning activities around my new home because I would do everything very differently depending on which way things go.

If useful, here's a rough outline of my situation and what I' hope to do if I could grab the field next door:
- What I have: I currently live on a 0.2 acre plot on the edge of a hamlet. It's basically a cottage and garden and driveway. I'm already turning what was the lawn into a food forest, with mixed "ornamental", pollinator and forage plants. I have the beginnings of some small annual veg plots elsewhere.
- The land I want: If my neighbours were willing to sell me half their field, it would more than triple the size of my property, so still small, but HUGE for me, and much more potential to do things.
- What I would probably do:
-- Access - Feasibility of owning half my neighbour's field would necessitate an access track from the road to their remaining section, through the section I want.
-- Trees - The field would be near 3 properties including us, so I'd never be able to go crazy as I'd risk blocking people's views, so I'd want to do something fairly constrained - a shelter belt of trees nearest our end so that I could build up a small patch of woodland density. Anything within the eyeline of other properties I was thinking might work as meadow with a few smaller orchard trees.;
-- Water - The patch I want goes down to a burn, which would be lovely. But I've seen a lot of scum (agri run off) on local burns too, so I would want a small pond that I could keep cleaner, with a view to maybe keeping ducks.;
-- Cover - I'm yearning for a small polytunnel or glasshouse. I'm thinking only an attractive glasshouse would NOT constitute an eyesore for my neighbours - haven't quite figured out how that bit might work or fit yet, but it does feel needed.;
-- Growing - I would want to cultivate annual veg and extend my food forest, but only on a subsistence scale. There would be NO active plan to sell market garden style or anything like that, though we might share or sell gluts if we ended up with any. I would also interplant pollinator species and some plants that might be construed as conventional "ornamental" (though it's highly unlikely that would be my primary reason for growing them). Basically, what I'd do might look a lot like a domestic garden, even if to me it felt like the closest I'll ever get to owning a farm.

NB. My neighbours have no idea of my designs on their field yet. But they're friendly, getting that bit older, and spend half their lives in Malaga, so they currently rent their field to a local farmer for haylage and I suspect find the amount of hedgecutting they have to do more of a burden than a joy. So I want to know if I'd ever be able to utilise a field first, and then find a way to raise the prospect with them. If they're not interested, there might be one or two other neighbours with sl. less ideal fields that I could also ask.

Sigh, why do they make it so complicated!

I'm by no means an expert, but here's a few thoughts for what they're worth.

Get on with your neighbours so they know what you are doing.

One form of protection may be to have some sales of goods. No matter how small, if you have a honesty box, or a monthly market stall then you are a producer of food, which ought to help. Keep records.

Talk to your local planning officers. There may be some support for production of local food, even if only for own use. You can do this informally. The laws generally are there to protect open land and prevent urban sprawl, so they may be able to advise on how likely you are to get permission for what you want to do.

Look into crofting laws. If the land is not currently a croft, you may be able to get it designated a croft and that is much more a household based land use I believe. Although this area of law as I understand it is very complicated, much less likely to be complained against. Often the crofts are owned by absentees and just go to bracken and semi feral sheep, which is supposed to be forbidden, but is rarely addressed.