I think you've put the main reason for your lack of motivation third on the list - depression, you can find away around the other reasons if the motivation was there.
I've always struggled when it comes to the scenery - I would begin my layout enthusiastically and then reach the scenic stage where my confidence would wain and before I knew it a new idea for a new layout took hold and off I went in a new direction. It was only last year that I finally accepted that I couldn't keep buying stuff for each new project and then see myself with too much stock and no railway to run it, then I sold off a good proportion of my stock.
During some counselling last summer I had an epiphany - my incessant need to purchase was dopamine driven, it was the thrill of the finding and making the purchase - once I got the item it lacked any thrill and then made me feel bad that I had bought something I didn't really need - it's a sign of an addiction.
I've also accepted that when I become obsessed with a new layout plan it is probably a sign that I am depressed and this is how I look inward into myself, falling back onto a comfortable pattern of behaviours.
What's changed in the past few months is that knowing why I purchase stuff and why I make plans that I wont actually deliver is part of repeating patterns of behaviour that do more harm than good. I've not purchased any railway stock since last summer, what I am buying in limited amounts are scenic items - paints, gravel etc and I am working towards finishing a railway and only once it is finished can I think about my next railway which will utilise some of my N stock.
Take the rest you owe yourself, sort out your head and then come back to modelling but pick something small and achievable, look at the Billy Bookcase threads - simple baseboard, simple track.
I typically use NHY581's Mutton as what can be achieved with simple track and baseboards, but I've also been looking a Ladmanlow sidings (Mutton inspired actually) as well
Can I also recommend you find yourself a local mindfulness or Buddhist group - those groups can transform people's lives.