I have an RSR 250 and RSR 525XL and are happy with both. 250 is 4YO and 525 is 1YO. As mentioned earlier the 250 has a chipboard stand but the quality is pretty good. The 525 has a plywood stand that is much better, but you won’t get that in either the 250 or 350. If it is available in either as an option now I would pay the extra and get it.
I have an RSK 600 in the 525 and it is great. I believe it is oversized for the 350 however so feel the RSK 300 is plenty, unless you are planning a really big bio load.
I run 3x RS90 lights on the 525 and they are great, so recommend those. Two should be enough in the 350, make sure you get the back hung arms to mount them, very clean. I run a Maxspect 420R triple on the 250, which is nice, but I don’t like the overhead straddle mount anywhere near as much as the RS90 mounts. Both lights grow corals just fine.
I run Gyres in both of my tanks - a single GP03 in the 250 and twin 350s in the 525. A single would be enough in the 350 and you could add in an MP10 or similar powerhead to deal with the dead spot you will have underneath it if that causes you an issue (it doesn’t cause me an issue in the 250).
Finally I recommend the larger tank IF you can afford it and IF your space will accomodate it. You will never regret a little more space in the tank, but you will also always regret getting a tank that is squeezed into to tight a space. Think about how much room you need for maintenance, backsides etc and then add 50% more for convenience.
Good luck!