Advice on new adopted dog training (Walking and barking)

Hi there, we have recently bought/adopted a 17 month old German Shepherd boy from a nearby town/city 4 days ago. He is a softie and very much a friendly boy.

However he is very much a puller on the leash when going for a walk, we use a harness for him with a 1-1.5m leash. So much so he pulls almost all of the time. I have been trying to use training treats to get him going, although I have only just started (today) and it showed some promise in the garden with just a short time (consiting of walking laps in the garden, when he says near and doesn't pull I give a treat with a "yes" and/or a "good boy", when he pulls, I tighten the leash and give no treat with a "here"), he doesn't seem to have the same promise when outside the house. (Assuming the sounds, smeels and more!)

He also seems to bark at anyone that comes near to chat or see him that he doesn't know except my partner and myself. They are quite the loud barks and I can see them potentially scaring people when he does it. This also happens when people are visiting or there are people at the door (even if he has seen them before) with the exception of my partner and me.

He wants to bound towards other dogs as well, larger dogs I think he wants to play wiht, on our first walk in a sort of dog prefered field he seemed to be very friendly to a black lab and the owner, the two jumping (and tangling) themselves. However he will whine and pull on the leash a lot when wanting to see other dogs, even when the dog / other owner shows no sign of wanting to interact (I get it! Not everyone does). On top of that the previous owner told us he was attack by a smaller Jack Russell when a bit younger, so that may be affecting some things?

I am considering 1-1 training with local trainer to see what they think. They offer group classes but I am unsure about going to those yet due to his "eagerness" to interact with other dogs, and that I have been told that a fair few of the dogs are pups.

I have currently only taken him out with my partner and it has been work just for a shorter walk. I will be needing to walking him myself in the mornings during the week as I work from home. However I am unsure if I should limit it to the garden while on my own and without any training to be safe or not?