I imagine that if the house orginally had frosted glass on the gable wall that it must be a condition of planning. So first step is to call into the local planning office.
Re the bins overflowing, being unsightly and smell, well this is bad form by the tenant. How about having a friendly chat with them. Maybe that would work.
Re the grass, do you know if it's the landlords or tenant's responsibility. You've also hinted there are other issues. Ultimately you could take ask the PRTB what action you could take against the landlord. This power is getting quite powerful. So firstly find out your rights and then a friendly call to the landlord might mean he will sort out the bins and grass.
You could also ask the owner if he is willing to go 50/50 on the costs of a wall, or seeing as you're in control of what gets built, 75/25. If he's a NE (negative equity) landlord you can forget it. Ultimately sounds like the wall will solve a lot of the problems you have.
Does your area have a residents association, they might be able to advise you also on what to do.