I think if you go too light you can correct that with a heavier buffer. I don't have huge experience with this, I don't do many builds and only one 300BLK build. I don't think it would be wrong to do as you intend, but my answers are always never that short. So here goes...
Mine uses a 10.3" barrel, but has the same pistol port location as yours. I used a JP Ent' full mass BCG. A standard weight buffer and standard buffer spring. I'm getting a correct ejection pattern @ about 4 O'clock.
More than that I don't have. Below are links so that you can compare what you have in mind to what I have working in mine if that will help.
My consideration was that the firearm must work in all temp's it's likely to encounter and I didn't want to go too far astray from the AR/M16 as it was designed. The basic design works pretty good without reinventing the wheel. Now if I had a specialized reason to change things up, like competition or some such I might have considered changing innards, but I just wanted it to function reliably without, again, special considerations.
But unless I miss my guess I'd be willing to bet a few million ARs have been built using semi-auto BCGs and they work fine. I think you might run into unforeseen issues if you go with too light a BCG, then you might need an adjustable gas block and other stuff not required on a more standard build.
https://www.ballisticadvantage.com/10-3 ... arrel.html
https://www.wingtactical.com/firearm-pa ... er-spring/
I had problems initially with cycling, but not due to anything other than a rifle buffer spring in the handgun. I cut off 3 coils and it worked fine. Now I have a flat wire carbine buffer spring in it and it works fine as long as I give it enough gas pressure. One issue that might be a problem for some... That flat wire spring appears to be "twangy" and it's been many decades since I notice buffer spring noise in the design. It doesn't bother me, it's just something I noticed but could bother others. Yeah, I know what the text at the link states. But I know what my ear picked up. Maybe I noticed it because it sounded differently. I don't know and didn't analyze it.