Not everyone has a bunch of spare time to jump on things right away. Even worse, when an issue gets snowballed into hundreds of different possible explanations - it's tough to choose which one to tackle first. Even tougher yet when you didn't build the car and haven't wrenched on vintage ones for many years. OP is willing and that's as important as anything else.
I think too many people are way too high on their horse. The OP bought a nice car, and paid people who seemed capable. After the fact, he learns he got shafted to some extent. It happens, but everyone throwing their $.02 in doesn't help. Also, he didn't build it so it's not like he has the knowledge of exactly what is what - he's having to research every damn thing. It's equivalent to buying someone else's project without a build summary or parts list. It takes a while to compile the 'simple' knowledge. Lots of us can rattle off exactly whats in our cars, but OP doesn't have that luxury at present.
There's a few questionable things on the car, like the regulator placement, but it's possible to put it there and do a neat job of it. That's not what his shop did, but it's not a priority to fix anymore since the leak is taken care of.
The throttle cable issue is a risky one. It's not just a matter of fixing the cable - the trans cable also needs to get setup properly. Get it wrong, and he could burn it up. I'd bet dollars to doughnuts the trans cable is holding the throttle from opening all the way, and that most other commentors don't even realize it's not a 727/904.
OP did try to address it and got it to open further but it's obvious the secondary butterflies still aren't getting actuated because they only open with the last 10-15% of throttle travel, and can also be limited by the choke system when those carbs are cold. I went looking to find a guide for OP to set this up properly, and lord help the newbie trying to find the info because it just isn't out there in an easy to digest form.
Give the OP a break or he's likely to simply disappear from the site. Being a business owner also comes with time demands and struggles, so it's not like he's going to be back on here a dozen times a day with updates like our more retired members get to LOL.