I just wanted to let you know....you're not alone. My first Sheltie, Miko was a godsend. EASY dog. I mean, even when he was a "wild" puppy, he was still overly good. He let me cut his nails at a young age, hated the bath, but got used to it, etc. He is my "Dark Perfection" that's his AKC name. lol.
Then, I bought Koji. Ohmigod. He was like the dog from hell. Or something. Seriously, his AKC name is "Outta My Mind". And well, I was!!! Like Samson, he was either off or on. Typical with puppies. I see you used my way too. Food. I started giving Koji a bully stick to chew on while I cut his nails. At 1.5, he barely stays still, so I give him a bully stick still. My hubby will hold it, or I"ll just get a long stick one, and stick it in his mouth. Oh, for some reason, it's easier for me to cut nails when they're on their back, worse for them, easy for me. Hence the food. But seriously, instead of making it a negative experience, I would suggest, when he's tired, to play with his feet, handle them, play with the nails, then treat him. Do it every night. That helped me a lot. Granted, again, bully stick helps more.
I'm not sure how soon crazy dogs slow down, but even at 1.5 Koji has a ton of energy. I'm waiting for him to "calm" down. lol. Although, for some reason, around 11-13 months, he did slow down a bit.
As for the potty thing. I will say this. Although you're on his schedule right now, let him learn how to hold it. We didn't do that with Koji, and it took us a VERY long time to teach him to hold it for more than 4-6 hours at a time. He was having accidents all the time if we didn't get home within that time frame. Very frustrating.
I think the best thing you can do is start training, or playing training games. I know that's what saved me a lot. I mean, everyone said it'd tire my dog out, but even now, my agility trainer says he'd probably keep going for another few hours. He's tired after, but he loves to train/eat/play. It helps them learn how to be better behaved. I think you got some great advice.
I know with Koji, he was really hard for me to deal with, especially after having Miko. Miko is probably the calmest Sheltie you'll ever meet and the easiest dog. Even 10 years later, he's very obedient, walks at a heel, perfect. lol. I wish I had done more training when Koji was younger, but to be honest, I was pulling out my hair at the time, and frustration was too high for me to deal with him. I'm regretting that now, as he's still a handful and so disobedient. He's WAY too smart for his own good.
Good luck. Sounds like you're doing well.
I didn't comment about the ears, because IMHO, it's a personal thing (if you're not showing). With Miko, I gave up. I didn't care if his ears were prick or not. With Koji, I tried so hard for a year, and yet, they're still prick. Sigh. Or at least one is. I could careless if my dogs ears are prick or not. The only reason I tried to keep Koji's correct, is because he's show quality (minus his height), and wanted him too look "correct". Oh well, I tried.
) Around six months she went the opposite direction, and is a pretty calm girl. Very nice, and loves to just sit in people's laps and be carried around.