overwhelmed owner: regression at 1 year old?

long post, apologizes in advance. welcoming all advice on any of these concerns.

my foxhound rescue has turned 1 year old as of this month (adopted at 5 months old) and after a some months of finding our groove and seeing great progress in our training, i’m noticing some regression/areas of concern. i’ve never owned a dog before, and am feeling a bit in over my head, similar to how i felt when we first got him. seeing constant positive dog training videos on instagram make me feel discouraged/like i’m failing, and like i have an insurmountable amount of work to do.

• we made big strides and was so proud of our growth over the past 2 months especially, but leash training has gone down hill again over the past 2 weeks. constant pulling is back with vengeance for some reason.

• he’s becoming toy possessive around his doggie friends (two dogs in our neighborhood he has played with almost daily since he got him), which was never the case before. he recently starting growling while playing tug for the first time this month, but it didn’t seem aggressive. it seemed as if he was just finding his voice. now he shows signs of aggression when another dog tries to get a toy that he has (much deeper growl, will gesture/nip to his dog friend to get away and is unwilling to share toys like he used to). he even gets this way when my partner tries to take a ‘high value’ toy from him now, too (he does well with me and responds to drop it command, but i WFH so i spend way more time with him/have a stronger relationship). is this normal? i know dogs are allowed to have boundaries/communicate to one another to back off, but i’m worried that these things will escalate as they seem to be, and my biggest fear is him biting or hurting any dog/person if we don’t address this ASAP.

• what are your thoughts on gentle leaders and Ecollars? do feel that entirely positive methods for dog training are realistic for you & your dog? do you feel there’s an air of shame around other forms of training?

• do you believe some dogs are just not able to be safely off leash, or can every dog get there with enough time and dedicated training?

• is regression real at this age, or just something we tell ourselves to take less accountability/help us feel better about our dog’s behavior?

• what more can i do? why do i feel like i’m never doing enough/intimidated by the sheer amount of work we have to do to have a “well trained/behaved” dog? do other dog owners feel this way?