Practice clipping in and out holding something and do not do as I did let go. At least that was the only wholly toppled over clipless moment I have had.
As to seat position what you need to look for is clipping in quite naturally without having to adjust your feet on the pedals. As you have two different fitting points on the shoes it may be that you need to try the other if you are not.
The cleats you have are quick release. Presumably they release by moving your foot away in any direction. Many do not like those as they find they unclip all too readily and prefer standard cleats with a more limited release action. I use one of each, the quick release on the foot I stop with.