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I would guess that the nitrogen to phosphorus ratio is off. Even if you fertilize, without the right amount of phosphorus, it will not bloom well. Bone meal is a great way to add phosphorus. This article will also help: https://www.gardeningknowhow.com/ornamental/vines/wisteria/wisteria-blooming-problems.htm

I would remove the old trellis as best you can and as long as you are not damaging any main trunks, you can remove some of the vine, if it will help. You can also leave some of the lattice attached as well. By this stage, your wisteria will be well established and will recover from any removed growth very quickly but will also engulf any broken lattice left behind pretty quickly as well. Once you set it against the new support, it will probably surprise you how quickly it will take to it.

This article will help with rooting the plant: https://www.gardeningknowhow.com/ornamental/vines/wisteria/propagating-wisteria-cuttings.htm The vine will not be a tree but you can (and should) grow it on a sturdy support. Here is more information: https://www.gardeningknowhow.com/ornamental/vines/wisteria/growing-wisteria-proper-wisteria-vine-care.htm

It sounds like you may have powdery mildew. This article will help you: https://www.gardeningknowhow.com/plant-problems/disease/get-the-cure-for-powdery-mildew.htm

I would guess that the nitrogen to phosphorus ratio is off. The soil may have an abundance of nitrogen, which would result in nice, healthy green growth but little to no blooms. Without the right amount of phosphorus, it will not bloom well. Bone meal is a great way to add phosphorus. This article will also help: https://www.gardeningknowhow.com/ornamental/vines/wisteria/wisteria-blooming-problems.htm

Wood lice typically feed on decaying material, so they are likely more a symptom of the problem, rather than the cause. The fact of the matter is that the plant may be just dying from old age. Plants, like animals, have a life span and your wisteria is certainly at a venerable age. But, you should try to do everything you can to save it. Ideally, you should have a horticulturalist take a look at it. At a basic level, treat the plant with a pesticide and a fungicide (neem oil is organic and is both a pesticide & fungicide). Plus, make sure it is getting the water and fertilizer it needs.