Ultimately, you have to try stuff. I would keep the two feet on the right to start with. Looks like you can gain nearly a foot on the left. Since there is not a wall close to the left speaker you have more space there. 6 feet apart would be a good sized triangle. You can try more later.
As far as the rack goes. In part it depends on the volume you listen. But I would try to move it as far away as possible so the speakers are not shaking the rack... I would try up to, but not under the TV. Good starting point. I am sure your wife doesn’t want this looking too weird.
Best practice... is to put the amp on the floor and split the system at the preamp. But, this is the kind of refinement you can work towards year from now. Yes, speaker cables should be the same length. We have all struggled with this. Frustrating, but a really good habit to bite the bullet and get the same length.
I’d recommend Robert Harleys, The Complete Guide to High End Audio. As if you would have time for reading with a toddler. I am sure you are lucky if you get a half hour to listen to music.
Also, it would be helpful to know your equipment. You can put that a Virtual System... so you don't have to repeat it. Knowing the exact components can be very helpful in making recommendations.
Have fun, take your time.
You’re welcome to PM me if you want to continue any of this in private. Your call. I’m good either way.