Hi everyone, I've rescued a beautiful 18 month old DS who has had a really tough time so far and I am his 5th owner and I'm not planning on him having any more homes! He's had no basic obedience training and he's not had any boundaries so he's a bit wild and obviously anxious as he's in a new environment. He's never been exercised which means that the past few days since he's been here, he's been on high alert on our walks and just dragged me up the mountain

he's very reactive to cars dogs and people and literally tries to throw himself at cars (dragging me into the road and pulling my arm out of the socket) he comes across as aggressive towards people but once they come to his level he is affectionate and quickly accepts them. He is very affectionate with us and seems to be binding well, in the past few days that we've had him, we've already seen some improvements with his obedience, he's definitely listening to cues and learning from positive reinforcement.
He is on extremely high alert and does not like being left alone, he has a bed food and water in the back porch and full access to the garden whilst we're at work, we have a camera so we can see and hear him, it was his first time being left alone today for a few hours and he cried a lot, I'm hoping that may get better once he's settled in with us.
I'm looking for any advice and reassurance from experienced owners in how to best train him, keep him stimulated and just any general advice. I understand I'm a newbie to a DS and there'll be people rolling their eyes at this post, but we all have to start somewhere and I'm definitely willing to out the effort in with him.
I have organised for a dog behaviouralist to come and assess him and help me with him in a few weeks time once he's settled.