Your splits look good, so you should be able to try kicking one foot at a time and the other will follow.
That's a very good point. If your splits are good, your guide leg (top leg) will be really close to the wall or pole or spotter anyway. Use the strength of your bottom leg/push-off leg to get your hips into position and then there's only just a little more to go for your guide leg/top leg to touch whatever is behind you. I would highly encourage you NOT to "kick up", but instead, push off the floor with that bottom leg and try to find your balance instead of forcefully crashing into the wall or pole. As for the arch: that's slightly more complicated, in my opinion. Some girls like to arch a lot to make a prettier line. I find that I have to arch a lot, because I'm so used to yoga-type handstands and I had a teacher scream at me to arch in order to get my sacrum to rest against the pole. This helped me (not the screaming but the advice!) because if I wanted to, say, grip the pole with my thighs and then sit up, I wouldn't have been able to unless I arched and got my tailbone closer to the pole. Whatever you choose to do, just make sure you engage your abdominals like mad in order to keep your body safe.