Just read back enormous post warning! 
The open spaces thing does sound a bit like insecurity. Do you know anything about his background?
As for meeting other dogs thing, I have no advice, as I have the same dilemma about whether/how to avoid the in yer face, rude dogs - and there do seem to be a lot of them about. When you say he gets reactive/excited, what does he actually do?
Lurcherboy recently started getting a bit bouncy when he saw other dogs while he was on the lead. He was doing a kind of stiff bodied pouncing up and down and I was worried it might be aggression, especially as he barked/bayed a couple of times too. He even seemed stalky with a couple of little dogs, which despite being a Lurcher, is totally out of character for him, so then I really started to fret that something was up. A few more walks - plus a course of eyedrops and realisation that both dogs had what was basically a doggie cold and I realised it was actually just over-excitement. Our old girls never really played with him and whilst they'd say a polite hello to dogs that approached them, were never interested in initiating interaction with other dogs in the park. Lurcherboy followed suit and pretty much ignored most dogs out and about. I think having Pip has made him realise the potential fun he could be having with other dogs, so now he just wants to go and play and gets over-excited/frustrated when he's on the lead because of it.
It could be that he's used to running loose with other dogs and find the lead frustrating, alternatively, being restricted by the lead might make him feel vulnerable, but it's so hard to tell without actually seeing him in action, iyswim.
You will get used to his body language and find it easier to read him, it just takes time. He won't have started to unpack his baggage yet and you will be somewhat on edge trying to do right by him and not make any mistakes. There will come a point where you both start to relax and one day you'll realise you've just had a lovely walk without even thinking about it.
... and you're not neurotic at all, you just care about your new boy. 
I have had a breakthrough with Pip today. I went out for coffee with my Mum and was gone for an hour and 15 minutes ... and Pip didn't make any noise, other than a little whine when the phone rang. The penny dropped last week that leaving him with enough treats and kongs etc to keep him busy meant that he needed to go out almost as soon as he finished eating and that's when he started making a racket.
With me having been quite ill over the last couple of months, he's got used to me shutting the kitchen door while I go for lie down and we managed to get up to them being in the kitchen for two hours with no problems - and no kongs etc. (Prior to that he would yell if I even went upstairs) So I decided to try doing the same, just shuting the door, leaving the TV on and leaving the house quietly - and it worked. 
Now I need to work on gradually building up the time and getting him used to the sounds of me leaving without them becoming negative signals.
It feels like a chink of hope, having been stuck at home pretty much since we lost Oldgirl, as first Lurcherboy had his stint of SA, then we ended up with a high-needs pup.
I was so worried it was me/something I'd done, having just been through it with Lurcherboy, but have been reassured, by someone I really respect to do with canine behaviour, that it's far more likely to be down to his difficult start in life. No mum from birth, then vets for a few days (touch-and-go) then surrogate mum but not for as long as most pups are with mum, then to the foster home. So no consistent mother-pup bond and three moves before he was more than a few weeks old, then he came to us and was really poorly = end result needy pup.
So we're finally getting there with him and I might be able to claw back a small fragment of an actual life!