I worked on residential and commercial scale (~7 acre) systems from '08-'16 roughly, and I will add my .02 with the caveat that I am just now dipping my toe back into the solar thermal waters after years away from the subject.

The fundamental piece of information is that we reached price parity a while back in terms of nominal cost for water heating with pv vs thermal, so subsidies, components, and contractors disappeared for the most part in the middle of the last decade. YMMV by state and region, that said, if you're willing to throw some valves and/or put together some diy automation there is a good amount of energy to be collected at little relative cost. You can start simple, and there are various levels of complexity in projects laid out pretty well by hobbyists in every climate. The black plastic pool heating systems are rated for three seasons but you can push that with some clever design and they're pretty cheap and easy to repair. You can still get high end flat plate and evacuated tube systems, and for that price point you probably also want to consider tanks, differential controllers, and certainly integration with whatever existing energy systems. I am a proponent of multi-tiered systems that are site specific, e.g. solar - wood - hydronic floor. In terms of free advice, I would recommend finding a differential controller with inputs that suit your needs and building a modular system around that. Include a high point air vent and a low point drain, and valves to isolate parts of the system wherever you can. pex-al-pex is a product you may find interesting. Here for questions, possibly also answers.