I've read through a fair bit of this but not every single post. However, I thought it might be helpful to add a few words as you sound quite upset and disempowered by the proceedings. This is your home, after all.
I have seen both sides of this - landlords coming in to take pictures, etc, including one memorable time when I walked in and realised my (own) living room furniture and ornaments had been completely rearranged in my absence to make it look better for the photos, without anyone telling me they were going in - how creepy is that? Doing a House Doctor with your tenants' personal stuff?!
I have also been a landlord a long time and had tenants being very quick to complain about repairs, maintenance etc, and then be awkward about letting people in to put things right, carry out routine inspections and so on. Recently I had some otherwise lovely tenants but they wanted the contract gardeners to fit their visits around two x three hour periods each fortnight when the woman might be there, and make a special arrangement on each occasion in advance. This is not only unrealistic, given that the contractors have 50 gardens to see to and it is weather dependent and so on, but also it was pretty cheeky as basically the reason we got them in was to put the garden right after the same tenants had rather let it go, and we were being nice and doing this at our expense. In advance of the end of their tenancy, we also needed to do some redecorations because of minor damage they had done with sellotape on the walls, chipped woodwork and so on, and then they complained about this being done before the end of their tenancy, and expected us to have a subsequent void and the next lot of tenants to move in late so that they wouldn't be put out in any way. I stress the works were not that intrusive, and we were only putting right damage they had needlessly (in my opinion) caused, and it was only an issue because the tenant insisted on always being there to stand and watch the workmen and refused to let us in while she was away on holiday ...
Anyway, I digress. I think it's reasonable to work with the landlord a bit as then everyone will be able to compromise. He or she does have the right to access for various things given the appropriate amount of notice, and it is difficult to market a property for rent without a single photo, so I personally think it's a fair to allow them in on one occasion at the least awful time of day to do this, having picked dirty washing up from the floor and done the washing up beforehand. Only once, mind. It is also reasonable to show people around the property now and then, by prior arrangement, before the end of the tenancy, as long as it's not excessive. If he or she is doing this too often, with insufficient notice, then it is probably reasonable to argue that it's a revolving door situation and too much to accommodate.
You also need to remember that you are in a business relationship here. It is perfectly legal for the landlord to give notice according to the terms in your contract, and to sell the house without you having a subsequent tenancy in place (i.e. forcing you to move). The key here is what your contract has said. It may be annoying or inconvenient, and perhaps tenancy law needs reforming, but that is where we are. In future, it is technically possible to arrange a contract that lasts for longer than 6-12 months or whatever, if you can find a landlord who prefers longer term lettings (I often do this for people - I am in the business of helping people have homes, not flipping properties). And of course you have the option of deciding to live in an area where you can afford to buy (in the past I have moved areas for precisely this reason). It sounds to me like you are fed up of renting and there may be a case for toying with the idea of settling down more permanently, even if it involves a move out of the area. In the meantime, try not to get into any fights with your landlord or agent as this will only cause you more stress and anxiety, believe me.