Two feet should work, but that's a guess. Maybe someone else with soffit lighting will comment.
Sure, you can do basic AI, somewhat advanced AI actually, with BI and DeepStack. The camera AI is a little different and can filter out false triggers generated by rain/snow/fog that normally trip motion detection in BI. That can be mitigated with DeepStack, but for best performance DeepStack needs a CUDA capable, NVIDIA based, video card for processing. A GTX1030, GTX1060, or a few others are the least expensive ones that will work well. Video cards have gotten extremely expensive with the pandemic and bots buying them up as soon as they hit the market.
I mentioned the 3241T-ZAS as an alternative if you want audio more than the AI features.