As for trading, I know what you are talking about and its a bit frustrating. I used to shop players around to see what kind of prospects I get, and the truth is that somehow, you only get players offered who make money... I tend to tailor a deal with the team that offers me the best MLB player... but even that is kinda stupid.
I think that started... last year?... when they wanted to fix the trade AI because rebuilding teams could be exploited too easy(like getting Jurickson Profar from the Rangers for some junk), as well as Win Now! teams prospect wise. Problem is, now you a.) can not easily who make money and aren't at least 4.5*, and b.) if you do, it takes you a ton of time to manually manufacture a trade. In your case, you also play in a league with 24 teams(instead of 30), which limits your trade options even more
That being said, I started to use this green/yellow/red information on the bottom more and more, and I found out that actually submitting a deal where they thing its close reveals some players that they don't name right away.
Something I exploit alot, and I'm not ashamed about is the fact that some teams, that have more starters than needed, but them in the pen as RP... and you can easily trade for them, change position to starter... and they double their trade value... so I basically trade for a RP, turn them into a SP and get back a way better package...
As for your problem with the minors DL thingy, go to your manager menu(the button on the top with the house), and select Team Control Settings. On the left, there should be a list of things that can get automized, like minor league demotions, roster management bla.... change that to your manager name and you should be fine... If not... I have no idea...