My original installation was an Austroflamm insert into a ZC fireplace, so maybe I can help with some free advice. The Austroflamm was twice the stove of what I could find to replace it. It lasted for a decade and a half when other contemporary stoves of similar pricing were lasting less than a decade. I never had any quarrel with the quality of the stove. I went with something different this time for a replacement (Austroflamms are not available in my corner of the country) and have regretted it; but that's my experience and MHO.
My avatar shows the current stove in the ZC fireplace. We have bricks underneath it to support the front, I had a custom piece of sheet metal bent to cover up that "make-do". Since you're putting in a new installation, consider that your stove will stick out of the fireplace for some length, and build yourself a strong and secure spot for the front feet to land. Having the front feet on something secure will also mean a quieter installation, since the stove will not transfer as much vibration back to the ZC fireplace box. (But Austroflamms are quiet anyway...) Also, we had to line the original ZC pipe with pellet stove pipe, and put a windproof cap on the top, replacing the cap and grating that was up there at the time. If this ZC is the way you're building your house, then start with a really high quality windproof cap up top, then you won't ever have to worry about an adapter up there which will eventually leak. We could tell the adapter was leaking when we heard the occasional 'bonk' of water dripping onto the top of the ZC box. I got a guy up there a dozen years ago and we did a belt-and-suspenders fix so that it will never leak again. And it hasn't - in spite of the very high winds and rough weather where we are. But start with yours done right.
Rika should have an online guide
like this one here that gives you clearances to combustibles. A little googling or a call to the Rika dealer (which you should do anyway) should yield the FPI book... The important point is that
every manufacturer will have a different set of measurements to combustibles. They will be similar measurements, but not the same. For the sake of your fire insurance, work from what the manufacturer says, and give it a few inches more if at all possible. Doing so will more than please your code inspector. One thing I can offer for advice: I would suggest keeping 30" hearthspace on the floor; this gives you space to sweep up pellets and ashes without ruining your flooring. Notice that mine is tile... It's that for a reason.
When we built our house 24 years ago, I had wanted a "stove alcove" as that would have been the most efficient way to heat the house, and it would have meant that we would have flexibility in whatever heat source we wanted to use. Three years into owning the ZC fireplace, we had a power outage with a snowstorm and high winds that lasted most of a week, and the house sank to 38° no matter how much wood I fed the fireplace. But we do have a fireplace... Just saying...
