Anxious puppy help/questions

Alright, a bit of a long intro here but it's all applicable to the question at hand so bear with me.

Saw our new addition to the family at a petsmart a few weeks ago. 7 m/o male mixed pup. Brought him home that day, and as we were getting him out of the truck, he slips his (shitty) 2-point harness and dips. Spent about 5-6 days running around, until finally someone was able to snag him up for us and we bring him home almost a week later and FINALLY, actually get him inside.

More background info on the dog – he appeared to be extremely anxious at the petsmart (understandable), and we were told he was incredibly shy around people, but loved other dogs. I've had dogs in my house for so many years that, we figured with the help of our other pup, we could show him he has nothing to be afraid of.

Fast forward, we're now 2 weeks into working with this dog. He has shown IMMENSE improvement. He will come up to myself and my wife on his own *sometimes*, for the most part he's potty trained (doesn't explicitly notify us yet but goes outside when let out), and he's now learned his new name. Additionally, he and our other pup are the BEST of friends. We have also just recently started to walk him on a leash and SECURE harness.

So, on to why I'm here. This poor pup is so severely anxious, that it makes ME anxious. Some times are definitely better than others, but for the most part.. he walks around with his tail tucked and the drop of a pin scares this little fella to death. We can't be anywhere near him when he's eating, else he runs in fear that he's doing something wrong? Not sure about this one. It's the opposite of food aggression as I spent the first few days hand feeding him to make sure that wasn't an issue. He will also take treats from our hand. Other things to note is that sometimes when called he will come to us, or other times he will spend 5-10 minutes running away from us. No, we don't chase him. But in order to get him to go outside to potty, or do whatever it is we need him to do, we have to position ourselves at a comfy distance away to kind of coax him in the desired direction. Leash and harness training has to start in the backyard as he is terrified of both and will typically dribble when he sees either. Once on the walk he seems fine though.

I'm looking for any advice y'all might have. Previous experiences, current, tips, tricks. Also wondering if anyone has tried anxiety meds with a younger pup as well. I had to give my older dog prozac and we saw a lot of success with that. Normally I wouldn't consider going straight to meds. However with how anxious and scared he is, it's hard to get through to him to work on training and other things.

My wife know that this is going to take time and a lot of patience. We have both. Hopefully from this we'll find out some extra things that'll help us along the way.