i might be right i might be wrong...but 2 weeks ago i was in your position. the way i scissor is i point my front foot 45deg to the the box-->then try to grip the edge of the box with the ski. it worked for me. basically go nice nd slow to start, feet wider apart is easier and play around with the angle of you front foot and moving it to the edge of the box.
when you edge ends up gripping on the box you will feel your rotation on the box stop and you start to be pulled around straight, then just pop off the box spin right land switch (for right foot forward).
correct me if im wrong, but forward food is always the driving foot, so always scisor with your front foot. if possible, the back foot will help, but when learning, the front foot is much easier to scissor and spin off of.
i always spin with my fwd foot. natural or unnatural. so #2 would be yes you have it right.
but there is a whole different technique fro blindside 270. those are possible to do without scssoring. just go on the jib overcrooked (more then 90) and pop and swing your arms to complete the spin.
does that help?
ok so i think this will help alot with frontside sw ups.
i spin left, so i will be describing this for a left spinning, right foot grinding person...
1 hop onto the right side of the box slightly, instead of straight onto the middle. land at about 45 degrees (makes it easier) ALREADY IN YOUR SCISSOR POSITION!!(front foot heel dropped) the longer the box, the less scissor you need. land on the box with knees slightly bent so it it easy to pop off.
2 pop! turn your HIPS and, so that you land with your head still looking down the hill, so that if you have another feature right after it, you can shred it, too!
i hope this helped!