I think you are too anxious about your child's safety.
The stair gate either is or isn't fit for purpose. If it isn't then you should remove it and replace it. Did the installer use wall anchors when putting it in?
The bedroom door gate could have been broken by someone swinging on it or standing on it and balancing, or pulling it further than it was designed to move. The damage wasn't necessarily malicious, just careless and heedless. Some kids are like that. It;s incredibly annoying and it feels as if you are hosting a tornado when they visit.
Rule of thumb for you for the future - children only play downstairs when they visit. There is too much scope for mischief if they play out of sight and earshot upstairs.
You mention this child played up 'as usual', so you should have supervised more closely.
My child has a habit of wandering blindly in the night and freaks out if I'm not there immediately
No matter how old your DC is, you need to work on this.
Getting a grip on your own anxiety here would be a good start. Stop being paranoid about stuff.
^Now I am having to sit up stairs all night down the hall to make sure of their safety because I need the person who originally put the gate on to come and redo it which obviously they can't tonight at this time.
Luckily I always have a drink bottle upstairs but I haven't eaten my tea yet, and while I don't mind not having it if it means my child is safe it's besides the point.^
This is actually batshit, not reasonable at all. Whoever has told you that you are overreacting is spot on.
Sitting upstairs and planning on bringing your child to bed with you is feeding the anxiety your child is experiencing. It is telling the child that there is something big and scary out there that he needs to be protected from. You can't assure your child that all is well in your home if you keep on pandering to all the anxiety that is swirling around, yours and theirs.
If your child is too young to negotiate stairs safely on their own, you could get a hook and loop kind of latch for your DC's door
www.amazon.com/National-Hardware-N187-034-Privacy-Rubbed/dp/B01EW1VM86/ref=asc_df_B01EW1VM86/?hvlocphy=9021569&linkCode=df0&hvptwo&psc=1&hvnetw=g&hvadid=194874485682&hvpone&hvlocint&hvpos=1o1&hvdev=c&hvdvcmdl&hvqmt&tag=mumsnetforu03-21&hvtargid=pla-313899936929&hvrand=8297586859217718420
They come in different lengths. You can install it high up on the door and frame. That way your child can sleep with the door slightly open but can't open it without standing on something. A monitor with two way communication capacity could help you communicate with your child to go back to bed if you see him/her getting up.
Your child needs to learn to stay asleep and not to wake up so fully in lighter sleep portions of the sleep cycle that he gets up and heads off to find you. Do not seek to manage this by adapting to it. You have to try solutions. Supernanny has some good ideas for sleep. Maybe the Behaviour or Sleep boards here could help too.
If you are generally so wound up about safety or anything else in your life, please see your GP. Anxiety can be treated.