I was not super-familiar with the Behringer Model D, but looking at it, it looks a little more semi than modular in the sense that you really don’t have patch point access to all parameters and you can’t break internal normalization so much.
Go full modular if that’s where your heart is! I definitely didn’t waste much time going down the rabbit hole once I started buying modules.
However, something like the O Coast is completely different animal, not just because of Make Noise’s philosophical bent and sound, but because nearly every internal connection can be overridden, and all the component parts can be used independently outside the O Coast if you want. Once your modular rack grows, the O Coast becomes a collection of useful utilities in a small package, if you’re not using it as a voice.
The O Coast also very explicitly labels all the normalizations on its panel, which shows you exactly how signal flow is moving, and therefore what normalizations you break when you patch it. It’s a very educational instrument.
Or again, go full modular, not going to necessarily advise you against it. But try to go slowly if you can. I used to think that advice was basically making a virtue of not having the budget to buy bigger systems (I’m a terrible person, at heart), and I will admit that buying a lot was the education on different modules I needed, given I didn’t have a Perfect Circuit or a Control or Control Voltage to visit and be hands on. But, I bought too much too fast, and it got overwhelming and to a point where I didn’t really know how my modules worked. Or, I would spend some time with one module, and then with another, and I would forget what I’d learned on the first one. I’m in the process of reeling it in, and I’m happier.