Hi, I empathize on sleep, the last three year has been extremely difficult to get quality sleep, and it amuses and annoys me when people say 'you need more sleep'! because if I could I would. sleeping past 5ish has been a challenge for me too.
1. yes apparently lack of sleep can stall weight loss. try taking magnesium to bowel tolerance before bed. ie start with 250-500mg its a natural muscle relaxant and most of us are deficient anyway. also vit d, taking 5000IU can help with sleep as well.
2. sleeping in is good as often as you can do it. for people with adrenal insufficiency its recommended even to sleep in between 7 and 9 as often as possible to aid recovery and healing of adrenals. not suggesting you are, but as an example of why more sleep is good.
3. goal setting has never worked for me in terms of sleep, its too much pressure. so some suggestions would be to try and be as relaxed as possible prior to bed, no tv in bed, lower lights to stimulate melatonin production, (or even take it)try and get to bed the same time each night. its a tough one, and different methods work better for all of us.
4. sleep deprivation can definitely effect the benefits of workouts and even the ability to workout maximally. speaking from experience when my sleep is really bad I feel like I am going backwards in the workout dept, which means its time to back off.
hope that helps and you can get more sleep!