I strongly agree with the suggestion of using a prefilter. Leaving waste in our systems for long periods has a negative effect on water quality. So if we allow our canisters to ingest waste, we should clean them often. But, if we use a prefilter to catch the solid waste, we can simply clean the prefilter (fast & easy) and service our canisters much less often.
As for filter placement... watch the tank. I rarely perfect my filtration to the point it removes all the debris. But, I do like for my filtration to consolidate the debris. Then I can come through a few times a week, siphon off a gallon or two of water getting rid of that consolidated debris. Since your set up doesn't have a strict "full" line, it'll make those spot checks even easier (since you don't have to top it off).
I generally use a lot of decor, rocks, slate, driftwood, etc, compared to your set up. With the small amount of decor you have breaking up your water flow, you'll likely be fine with what you have. If you don't like where waste/debris settles, move your intakes/outputs around, or add a powerhead.
We can give you input all day, and you'll get a wide range from us. But you're the one looking at your tank. You see what your current level of filtration is doing. And you'll be the one supplementing debris clean up that the filter doesn't get. So as long as you've got basic water movement (i.e. no dead spots) throughout the tank, it's really personal preference after that.
And then, no matter what you decide, someone will come along to critique it. lol.