Life with Marley and Oski - plus more questions :)

Thank you all for the compliments and advice in my previous post about bringing our new doodle, Oski into our home. I didn't know much about Australian Labradoodles before getting him and I've been reading up about the history of the breed and I feel so lucky that we got him as his specific ancestry is pretty fascinating.

Night #2 was much better, I had him in the crate a few times in the afternoon and then at night around 11pm he went in and cried for about 15 min and then slept until I woke him up at 3:30 (because I had to get up for work), I am guessing he would have lasted longer had I not disturbed him. Marley did not keep us up, she settled back to her usual routine of sleeping in our girls' room.
Wednesday was the day he was to be at home alone while we were all out at work. This didn't go so well, although it could have been worse. My husband was running late and rushing and so he asked our 8 year old to close the baby gate to keep him in our master bath vanity area with his crate and then shut the bedroom to keep Marley out. He did not check to see how she did this. He came home from work in the evening to find that Oski had been busted out (Marley can often push the bedroom door open if it's not shut tight) and the baby gate was down (it's the tension kind and I think it wasn't quite set tight enough). The house was not totally destroyed but there were a few little gifts of poop. I know it could have been worse since he didn't chew anything up and I can probably thank Marley for that since they most likely just played and played and napped. But it definately was a set back in housebreaking since he was able to freely poop without correction.
Night #3 was even better, I put him in his crate several times in the evening when we were eating and dealing with bath and bedtime for the girls. I did miss his que when he needed to poop, but I scooped him up to correct it when caught him. Then again in the crate at 11pm but this time in the living room while I sat and watched some tv. His crying was much less than before and he went to sleep and so when I went to bed, I left the crate where it was and he didn't wake up at all until 6am.

Now for questions
Using a collar and/or leash- Some people have mentioned tethering a puppy to keep a close eye on them. But thought he was too young to wear a color or be on a leash? I feel like I read that somewhere. He's 10 weeks. Please explain.

I've been at home all day and haven't put him in his crate. He sticks close to me and we're making trips outside to run around and go potty. (Although I admit I have missed a few ques or let him wander out of my eyesight, so I have to work on that.)
He and Marley alternate between laying around napping or playing and chewing rawhide rolls. And then playing fighting over the same roll and so and so forth. Should I be crating him a few times throughout the day just for consistancy or only as needed?

I'm having trouble making Oski eat his food and Marley eat hers. They seem to like to trade. How much does this matter?

Thanks!!