....did Gordon really think Bud would be OK with him (1) shattering his well thought out plan of building the company, but more over (2) putting his dad out of a job and (3) screwing over people Bud had grown up around and was clearly still on good terms with.
Bud is quite visibly and verbally angry when he confronts Gekko about it, yet all he does is ask "are you with me?" - and after a reluctant and insincere "yes", Gordon seems to think "good enough".
It's hard to believe his judgement could be so off.
Gordon didn't care whether Bud would be okay with it. Gordon did what he wanted, and assumed that Bud was powerless to stop him.
What bugs me is that Bud knew that Gordon had become wealthy by buying and selling, even if companies were destroyed and people lost their jobs. Why did he think that Gordon's behaviour would change in the case of Bluestar?
To your second point, I never bought the premise of Bud suddenly wanting to buy and rebuild Blue Star in the first place. He was roaring along buying and selling stock with inside information and making a huge fortune. They never broke down Bud's financial gains in the movie so we'll never know how much he was worth by the time he suddenly aspired to be a CEO stiff for a unionized mid-size national airliner but it had to run counter to what he was already doing and as it plays out, Stockwatch was finally sensing suspicious activity from his transactions.
I believe Stone wanted to sell the idea that Bud believed that he was so smart being a successful insider trader that he could parlay that success into doing the straight and narrow by orchestrating a stock takeover of BlueStar and revamping its operations and marketing tactics. To me it doesn't really add up because Bud is rocking along making bank on his insider trading. If Stone wanted to sell us the idea that Bud felt guilty and that he was still human with a conscience then he did it ever slow slightly, if not unconvincingly, at least for me.
There are small scenes where Bud has self-reflection like after he bangs Darrien in his new gaudy apartment and sits outside in his balcony contemplating life, then there's a small scene where we see Bud stressing because he seems to be in over his head with "spreading out his trades" to avoid red flags, but it's not elaborated on that perhaps he wants to go the legal and straight road. Either way, it was funny seeing Bud pitch his highschool-level business class "3 Point Plan" to the BlueStar Union and Executives and actually sell it.
No matter how greedy Gordon is, his decision to destroy Bud's father's company is irrational. Therefore, I don't see Buck's decision to trust Gordon as a wrong decision on paper. Both are business partners, and damaging Bud's father's business could get Gordon into trouble, which actually happened. This is a poor business decision. Bud has all the reasons in the world to believe that Gordon will keep his father's company alive.
Furthermore, it turns out that Gordon is less adept at reading people than initially assumed. He believed that Buck was ambitious and uninhibited enough to harm his family. If he had separated the business partnership with Buck from Buck's family and friends, it is likely that Buck would have continued to bend the law to make money, avoided taking stock about his life, and certainly would not have turned against Gordon.
I don't think it mattered to Gekko that Bud had personal relations to people at Bluestar. He told Bud that his father would never have to work another day in his life. He was trying to buy Bud into the idea that sometimes you don't have to follow moral or social traditions to succeed in life, such as working honestly to earn your resources, and that sometimes people will take losses at the hands of others.
This is what set Bud apart from him; he was willing to get his hands dirty as long as nobody in his circle suffered long-lasting consequences and damage, but he was too naive to realize that Gekko had no problem screwing over anyone at all to get what he wanted, including Bud himself, as he legitimately wanted to turn Bluestar around, while Gekko had other plans, likely from the beginning of being pitched the idea.