8 year Soto Zen buddhist here with formal practice, can't pretend to offer the correct scholarly answer but I'll share my point of view.
>1) Although any given object is impermanent, isn't it still possible to stay abstractions are? A ball is impermanent, but the notion of roundness is not.
You're onto something but kind of going half-way here. You have to understand the nature of physical phenomena in order to grasp the meaning of impermanence, which is intimately connected to the theory of dependent origination; that things arise in dependence on conditions. Abstractions are dependent on intellectual awareness, which I'm sure we all can agree is impermanent. In the Lankavatara sutra, however, it is said that Buddha-knowledge is permanent due to being independent and timeless. It could be construed as a kind of abstraction, depending on your point of view, but one should be inclined to view ultimate enlightenment as distinct from the sphere of "ordinary " thoughts.
>2) If Samsara is beginningless, would it be fair to say the only thing that is permanent in Becoming is Becoming itself?
Becoming has an end in nirvana. That's the whole point of Buddhism. It is said, since the Pali canon, that Samsara's origin cannot be discerned, but it is not endless.
>3) a) Existence is a process, not a thing b) Abstract categories, qualities, properties etc. are the patterns in this process c) Ergo, patterns are permanent, although still conditioned and certainly not a viable object of enlightenment and transcendence
In Buddhism we speak of all perceivable phenomena as dharmas, which is difficult to translate into layman's terms but roughly equates to mental events. It's very helpful to keep the term "event" in mind, since all things are events and, as such, processes as well, precisely because they are impermanent. That includes abstractions and other "patterns " dependent on human intelligence.